<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>10301 - Disclosure - Liquidity</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><CurrencyCode /><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName /><CurrencySymbol /><contextRef><ContextID>Duration_7_1_2012_To_6_30_2013</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0000882873</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2012-07-01T00:00:00</PeriodStartDate><PeriodEndDate>2013-06-30T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS /><CurrencyCode /><OriginalCurrencyCode /></MCU><CurrencySymbol /><Labels><Label Key="CalendarSupplement" Id="0" Label="12 Months Ended" /><Label Key="Calendar" Id="1" Label="Jun. 30, 2013" /></Labels></Column></Columns><Rows><Row FlagID="0"><Id>1</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>1</Level><ElementName>ulgx_LiquidityAbstract</ElementName><ElementPrefix>ulgx_</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Liquidity [Abstract]</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>ulgx_LiquidityDisclosureGoingConcernNoteTextBlock</ElementName><ElementPrefix>ulgx_</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>terseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="Duration_7_1_2012_To_6_30_2013" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div&gt; &lt;div style="margin-left:0pt;margin-right:0pt;"&gt;
		&lt;p style="margin:0pt 0pt 10pt 18pt;text-indent:-18pt;font-family:Palatino;font-weight:bold;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;font-family:Times New Roman;font-size: 11pt"&gt;
			&lt;font style="text-indent:0pt;margin-left:0pt; width:36pt;"&gt;&lt;font style="display: inline;font-weight:bold;font-size:11pt;"&gt;3.&lt;/font&gt;&lt;/font&gt;&lt;font style="text-indent:0pt;margin-left:0pt; width:-1pt;text-align:left"&gt;&lt;font style="display: inline;font-weight:bold;font-size:11pt;"&gt;Liquidity&lt;/font&gt;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;line-height:normal;font-family:Times New Roman;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;font-family:Times New Roman;font-size: 10pt"&gt;
			&lt;font style="text-indent:0pt;margin-left:0pt; width:36pt;"&gt;&lt;/font&gt;&lt;font style="text-indent:0pt;margin-left:0pt; width:-1pt;text-align:left"&gt;&lt;font style="display: inline;font-size:10pt;"&gt;At June 30, 201&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;3&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;, the Company had cash and cash equivalents of $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;2,290&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;,&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;000&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;.&amp;nbsp;&amp;nbsp;The Company incurred net losses of $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;4,292&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;,000 in fiscal year 201&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;3&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; and $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;4,695&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;,000 and $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;3,733&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;,000 in the fiscal years ended 201&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;2&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; and 201&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;1&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;, respectively.&amp;nbsp;&amp;nbsp;In addition, the Company has accumulated aggregate net losses from the inception of business through June 30, 201&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;3&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; of $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;119.0&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; million&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;.&amp;nbsp; &lt;/font&gt;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;line-height:normal;font-family:Times New Roman;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;font-family:Times New Roman;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-size:10pt;"&gt;During the first quarter of fiscal 2012, the Company entered into a license agreement with Medtronic for the Prostiva RF Therapy System. The Company paid Medtronic $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;500,000&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; on September 6, 2011 for half of the $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;1,000,000&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; initial license fee, with the remaining $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;500,000&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; payable on the one-year anniversary of this date, September 6, 2012.&amp;nbsp; &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;On June 28, 2013, we entered into a Restructuring Agreement with Medtronic related to the $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;7.5&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; million we owed to Medtronic under the Transaction Documents.&amp;nbsp;&amp;nbsp;As part of this agreement we paid Medtronic $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;2.0&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; million in satisfaction of royalties earned for the 12 months ended September 6, 2012, the second half of the initial licensing fee, the license maintenance fee for the 12 month period ended September 6, 2012, for outstanding transition services fees, and for Prostiva inventory included as part of the acquisition and purchased subsequent to the acquisition.&amp;nbsp;&amp;nbsp;In addition, we entered into a promissory note (the &amp;#x201C;Note&amp;#x201D;) with Medtronic for $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;5.3&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; million for the remaining amounts owed on Prostiva inventory acquired as part of the acquisition and purchased subsequent to the acquisition.&amp;nbsp;&amp;nbsp;Interest on the Note will accrue at a rate of &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;6&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; percent, compounded annually and is payable in five equal installments of principal plus accrued interest on March 31&lt;/font&gt;&lt;sup style="display: inline;font-size:10pt;"&gt;st&lt;/sup&gt;&lt;font style="display: inline;font-size:10pt;"&gt; of each year beginning on March 31, 2015. The $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;206,000&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; difference between the $7.5 million in obligations owed to Medtronic and the $2.0 million paid and the $5.3 million Note was recorded as a gain on debt extinguishment.&amp;nbsp; &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;line-height:normal;font-family:Times New Roman;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;font-family:Times New Roman;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-size:10pt;"&gt;During the first quarter of fiscal 2013, the Company completed a follow-on offering in which we sold &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;5,980,000&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; shares of common stock at a price of &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;$0.75&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; per share which contributed approximately &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;$&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;3.8&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; million of net proceeds&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; after deducting underwriting discounts and commissions and other expenses payable by the Company.&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; &amp;nbsp; &amp;nbsp;&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;However, as a result of the Company&amp;#x2019;s history of operating losses and negative cash flows from operations, &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;and the need for additional working capital to support future operations&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;, there is substantial doubt about our ability to continue as a going concern.&amp;nbsp; The Company&amp;#x2019;s cash may not be sufficient to sustain day-to-day operations for the next 12 months. The Company&amp;#x2019;s ability to continue as a going concern is dependent upon our ability to generate positive cash flows from our business, maintain available borrowing under our line of credit with Silicon Valley Bank entered into on January 11, 2012, as amended on November 30, 2012 and aggressively manage our expenses, including those associated with our acquisition of the Prostiva product li&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;ne from Medtronic.&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;The line of credit &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;with Silicon Valley Bank &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;allows borrowing by the Company of up to the lesser of $&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;2.0&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; million or the defined borrowing base consisting of &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;80&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;% of eligible accounts&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; receivable. As of June 30, 201&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;3&lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt; the Company has not borrowed against this facility. &lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;line-height:normal;font-family:Times New Roman;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;font-family:Times New Roman;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-size:10pt;"&gt;There is no assurance that our cash, cash generated from operations, if any, and available borrowing under our agreement with Silicon Valley Bank will be sufficient to fund our anticipated capital needs, operating expenses, and Note repayments, particularly if product sales do not generate revenues in the amounts currently anticipated, if our operating costs are greater than anticipated or greater than our business can support. &lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;font-family:Arial Unicode MS;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;font-family:Times New Roman;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-size:10pt;"&gt;The Company&amp;#x2019;s current plan to improve its cash and liquidity position is to generate expected revenues both from sales of our Cooled ThermoTherapy and Prostiva products which will help generate improved cash flow from our business.&amp;nbsp;&amp;nbsp;In addition, &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;management adopted a cost reduction plan which calls for cuts in planned spending and expense in nearly all departments.&amp;nbsp; &lt;/font&gt;&lt;font style="display: inline;font-size:10pt;"&gt;The Company may also seek to improve its liquidity position by raising capital through additional indebtedness or an offering of its equity securities or both.&amp;nbsp;&amp;nbsp; &lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;border-bottom:1pt none #D9D9D9 ;font-family:Arial Unicode MS;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;border-top:1pt none #D9D9D9 ;border-bottom:1pt none #D9D9D9 ;font-family:Arial Unicode MS;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt;If the Company is unable to generate sufficient liquidity to meet its needs and in a timely manner, the Company may be required to further reduce expenses and curtail capital expenditures, sell assets, or suspend or discontinue operations. If the Company is unable to make the required payments to Medtronic with respect to the Prostiva acquisition&lt;/font&gt;&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt; or the Note&lt;/font&gt;&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt;, it would give Medtronic the right to terminate the Company&amp;#x2019;s rights to sell the Prostiva product.&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;border-top:1pt none #D9D9D9 ;border-bottom:1pt none #D9D9D9 ;font-family:Arial Unicode MS;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;border-top:1pt none #D9D9D9 ;border-bottom:1pt none #D9D9D9 ;font-family:Arial Unicode MS;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt;The financial statements as of and for the year ended June 30, 201&lt;/font&gt;&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt;3&lt;/font&gt;&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt; do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classifications of liabilities that may result should the Company be unable to continue as a going concern.&lt;/font&gt;
		&lt;/p&gt;
		&lt;p style="margin:0pt;text-indent:36pt;border-top:1pt none #D9D9D9 ;font-family:Arial Unicode MS;font-size: 10pt"&gt;
			&lt;font style="display: inline;font-family:Times New Roman;font-size:10pt;"&gt;&amp;nbsp;&lt;/font&gt;
		&lt;/p&gt;
		&lt;p&gt;&lt;font size="1"&gt; &lt;/font&gt;&lt;/p&gt;
	&lt;/div&gt; &lt;/div&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>Disclosure regarding substantial doubt about an entity's ability to continue as a going concern for a reasonable period of time (generally a year from the balance sheet date), disclose: (a) pertinent conditions and events giving rise to the assessment of substantial doubt about the entity's ability to continue as a going concern for a reasonable period of time, (b) the possible effects of such conditions and events, (c) management's evaluation of the significance of those conditions and events and any mitigating factors, (d) possible discontinuance of operations, (e) management's plans (including relevant prospective financial information), and (f) information about the recoverability or classification of recorded asset amounts or the amounts or classification of liabilities.</ElementDefenition><ElementReferences>No definition available.</ElementReferences><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Liquidity</Label></Row></Rows><Footnotes /><IsEquityReport>false</IsEquityReport><ReportName>Liquidity</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>true</HasCustomUnits><IsEmbedReport>false</IsEmbedReport><IsMultiCurrency>false</IsMultiCurrency><ReportType>Sheet</ReportType><RoleURI>http://www.abc.com/role/DisclosureLiquidity</RoleURI><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows></InstanceReport>
