<?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>104 - Disclosure - LINE OF CREDIT</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

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</LabelSeparator><Level>1</Level><ElementName>us-gaap_LineOfCreditFacilityAbstract</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</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>LINE OF CREDIT [Abstract]</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>hiit_LineOfCreditFacilityTextBlock</ElementName><ElementPrefix>hiit_</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="from-2013-01-01-to-2013-06-30.2486.0.0.0.0.0.0.0" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;!--DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" --&gt;&lt;div&gt; &lt;div style="WIDTH: 624px"&gt;&lt;!--StartFragment--&gt; &lt;p style="MARGIN: 0px"&gt;&lt;strong&gt;NOTE 4 - LINE OF CREDIT&lt;/strong&gt;&lt;/p&gt; &lt;p style="MARGIN: 0px"&gt;&lt;br /&gt; &lt;/p&gt; &lt;p style="MARGIN: 0px"&gt;On June 26, 2013, our wholly-owned subsidiaries, KMHVC, Inc. and AES (the "Borrower") entered into a $2 million revolving accounts receivable financing facility with Rosenthal &amp;amp; Rosenthal ("Rosenthal"). The financing facility provides for the Borrower to have access to the lesser of (i) $2 million or (ii) 85% of Net Amount of Eligible Receivables (as defined in the financing agreement). The financing facility is paid for by the assignment of the Borrower&amp;#39;s accounts receivable to Rosenthal and is secured by the Borrower&amp;#39;s assets. The financing facility has an interest rate of 4.00% in excess of the prime rate reported by the Wall Street Journal per annum. The interest rate increases to the prime rate plus 7.00% for any borrowings in excess of 85% of the Borrower&amp;#39;s Net Amount of Eligible Receivables. In addition, the Borrower paid Rosenthal a facility fee of $30,000 on the closing and an annual fee of $20,000 and a monthly administration fee of $1,000 as well as monthly additional charges of not less than $2,000. The financing facility is for an initial term of two-years, expiring on June 30, 2015, and will renew on a year to year basis, unless terminated in accordance with the financing agreement. If the facility is terminated prior to the first anniversary, Borrower is obligated to pay Rosenthal a fee of $40,000 and if terminated after the first anniversary and prior to the second anniversary then Borrower shall pay a fee of $20,000. We guaranteed repayment of the line of credit, which guaranty is secured by our assets.&lt;/p&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;p style="MARGIN: 0px"&gt;During the six months ended June 30, 2013, the Company made draws, net of expenses of $934,200, as of June 30, 2013.&lt;/p&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;&lt;/p&gt; &lt;p style="MARGIN: 0px"&gt;Pursuant to the terms of the financing facility, the Company is required to maintain at the end of each quarter, tangible net worth in an amount not less than negative $1,000,000 and working capital of not less than negative $2,000,000.&lt;/p&gt; &lt;p style="MARGIN: 0px"&gt;&lt;br /&gt; &lt;/p&gt; &lt;p style="MARGIN: 0px"&gt;The Company paid a total of $63,700 in various financing fees which will be amortized over the two year life of the line of credit. &amp;nbsp;A summary is shown below:&lt;/p&gt; &lt;p style="MARGIN: 0px"&gt;&lt;br /&gt; &lt;/p&gt; &lt;table style="FONT-SIZE: 10pt; MARGIN-TOP: 0px" cellspacing="0" cellpadding="0"&gt; &lt;tr style="FONT-SIZE: 0px"&gt; &lt;td width="64"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="64"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="64"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="88"&gt;&amp;nbsp;&lt;/td&gt; &lt;td width="67"&gt;&amp;nbsp;&lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="192" colspan="3"&gt; &lt;p style="MARGIN: 0px"&gt;Balance at January 1, 2013&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="88"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="67"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;&amp;nbsp;$ &amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;- &amp;nbsp;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="192" colspan="3"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;Add: &amp;nbsp;financing fees paid&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="88"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="67"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt; &amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;63,700&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="280" colspan="4"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;Less: &amp;nbsp;amortization of deferred financing costs&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-BOTTOM: #000000 1px solid; MARGIN-TOP: 0px" valign="bottom" width="67"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt; &amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;- &amp;nbsp;&amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="64"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="64"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="64"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="88"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="67"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt; &amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;63,700&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="192" colspan="3"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;Less: &amp;nbsp;current maturities&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="88"&gt; &lt;p style="PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 0px; PADDING-RIGHT: 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;/td&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="67"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;&amp;nbsp;&amp;nbsp;(31,850)&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td style="MARGIN-TOP: 0px" valign="bottom" width="280" colspan="4"&gt; &lt;p style="MARGIN: 0px"&gt;&amp;nbsp;Long-term deferred financing costs&lt;/p&gt; &lt;/td&gt; &lt;td style="BORDER-TOP: #000000 1px solid; BORDER-BOTTOM: #000000 3px double; MARGIN-TOP: 0px" valign="bottom" width="67"&gt; &lt;p style="MARGIN: 0px; text-align: right"&gt;&amp;nbsp;$ 31,850&lt;/p&gt; &lt;/td&gt; &lt;/tr&gt; &lt;/table&gt; &lt;!--EndFragment--&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>No authoritative reference available.</ElementDefenition><ElementReferences>No definition available.</ElementReferences><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Line of Credit</Label></Row></Rows><Footnotes /><IsEquityReport>false</IsEquityReport><ReportName>LINE OF CREDIT</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.hiitinc.com/role/LineOfCredit</RoleURI><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows></InstanceReport>
