<?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>060600 - Disclosure - INVENTORY</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_InventoryDisclosureAbstract</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>INVENTORY [Abstract]</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>us-gaap_InventoryDisclosureTextBlock</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><PreferredLabelRole>verboseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="c20130101to20130630" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="font-family: 'Times New Roman', Times, serif; font-size: 10pt;"&gt;&lt;div&gt;&lt;table cellpadding="0" cellspacing="0" style="width: 100%; font-family: times new roman; font-size: 10pt;"&gt;&lt;tr&gt;&lt;td align="left" valign="top" style="width: 9%;"&gt;&lt;div style="text-align: left; text-indent: 0pt; display: block; font-family: Times New Roman; margin-left: 0pt; font-size: 10pt; font-weight: bold; margin-right: 0pt;"&gt;NOTE 6.&lt;/div&gt;&lt;/td&gt;&lt;td align="left" valign="top" style="width: 91%;"&gt;&lt;div style="text-align: left; text-indent: 0pt; display: block; font-family: Times New Roman; margin-left: 0pt; font-size: 10pt; font-weight: bold; margin-right: 0pt;"&gt;INVENTORY&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt;&lt;/div&gt;&lt;div style="text-indent: 0pt; display: block;"&gt;&lt;br /&gt;&lt;/div&gt;&lt;div style="text-align: justify; text-indent: 0pt; display: block; font-family: Times New Roman; margin-left: 0pt; font-size: 10pt; margin-right: 0pt;"&gt;As of June 30, 2013, our inventory was comprised of Altrazeal&amp;#174; finished goods, manufacturing costs incurred in the production of Altrazeal&amp;#174;, and raw materials.&amp;#160;&amp;#160;Inventories are stated at the lower of cost (first in, first out method) or market.&amp;#160;&amp;#160;We regularly review inventories on hand and write down the carrying value of our inventories for excess and potentially obsolete inventories based on historical usage and estimated future usage.&amp;#160;&amp;#160;In assessing the ultimate realization of our inventories, we are required to make judgments as to future demand requirements.&amp;#160;&amp;#160;As actual future demand or market conditions may vary from those projected by us, adjustment to inventories may be required.&lt;/div&gt;&lt;div style="text-indent: 0pt; display: block;"&gt;&lt;br /&gt;&lt;/div&gt;&lt;div style="text-align: justify; text-indent: 0pt; display: block; font-family: Times New Roman; margin-left: 0pt; font-size: 10pt; margin-right: 0pt;"&gt;The components of inventory, at the different stages of production, consisted of the following at June 30, 2013 and December 31, 2012:&lt;/div&gt;&lt;div style="text-indent: 0pt; display: block;"&gt;&lt;br /&gt;&lt;/div&gt;&lt;div&gt;&lt;table cellpadding="0" cellspacing="0" style="width: 100%; font-family: times new roman; font-size: 10pt;"&gt;&lt;tr&gt;&lt;td align="left" valign="bottom" style="border-bottom: black 2px solid;"&gt;&lt;div style="text-align: left; text-indent: 0pt; display: block; font-family: times new roman; margin-left: 0pt; font-size: 10pt; font-weight: bold; margin-right: 0pt;"&gt;Inventory&lt;/div&gt;&lt;/td&gt;&lt;td align="right" valign="bottom" style="padding-bottom: 2px; font-family: times new roman; font-size: 10pt; font-weight: bold;"&gt;&amp;#160;&lt;/td&gt;&lt;td align="right" colspan="2" valign="bottom" style="border-bottom: black 2px solid;"&gt;&lt;div style="text-align: right; text-indent: 0pt; display: block; font-family: times new roman; margin-left: 0pt; font-size: 10pt; font-weight: bold; margin-right: 0pt;"&gt;June 30, 2013&lt;/div&gt;&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; padding-bottom: 2px; font-family: times new roman; font-size: 10pt; font-weight: bold;"&gt;&amp;#160;&lt;/td&gt;&lt;td align="right" valign="bottom" style="padding-bottom: 2px; font-family: times new roman; font-size: 10pt; font-weight: bold;"&gt;&amp;#160;&lt;/td&gt;&lt;td align="right" colspan="2" valign="bottom" style="border-bottom: black 2px solid;"&gt;&lt;div style="text-align: right; text-indent: 0pt; display: block; font-family: times new roman; margin-left: 0pt; font-size: 10pt; font-weight: bold; margin-right: 0pt;"&gt;December 31, 2012&lt;/div&gt;&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; padding-bottom: 2px; font-family: times new roman; font-size: 10pt; font-weight: bold;"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="#cceeff"&gt;&lt;td align="left" valign="bottom" style="width: 76%;"&gt;&lt;div style="text-align: left; text-indent: 0pt; display: block; font-family: times new roman; margin-left: 0pt; font-size: 10pt; margin-right: 0pt;"&gt;Finished goods&lt;/div&gt;&lt;/td&gt;&lt;td align="right" valign="bottom" style="width: 1%; display: inline; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;$&lt;/td&gt;&lt;td valign="bottom" style="text-align: right; width: 9%; font-family: times new roman; font-size: 10pt;"&gt;112,984&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td align="right" valign="bottom" style="width: 1%; display: inline; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;$&lt;/td&gt;&lt;td valign="bottom" style="text-align: right; width: 9%; font-family: times new roman; font-size: 10pt;"&gt;303,779&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="white"&gt;&lt;td align="left" valign="bottom" style="width: 76%;"&gt;&lt;div style="text-align: left; text-indent: 0pt; display: block; font-family: times new roman; margin-left: 0pt; font-size: 10pt; margin-right: 0pt;"&gt;Work-in-progress&lt;/div&gt;&lt;/td&gt;&lt;td align="right" valign="bottom" style="width: 1%; display: inline; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="text-align: right; width: 9%; font-family: times new roman; font-size: 10pt;"&gt;357,104&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td align="right" valign="bottom" style="width: 1%; display: inline; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="text-align: right; width: 9%; font-family: times new roman; font-size: 10pt;"&gt;190,794&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="#cceeff"&gt;&lt;td align="left" valign="bottom" style="padding-bottom: 2px; width: 76%;"&gt;&lt;div style="text-align: left; text-indent: 0pt; display: block; font-family: times new roman; margin-left: 0pt; font-size: 10pt; margin-right: 0pt;"&gt;Raw materials&lt;/div&gt;&lt;/td&gt;&lt;td align="right" valign="bottom" style="padding-bottom: 2px; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="border-bottom: black 2px solid; text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="border-bottom: black 2px solid; text-align: right; width: 9%; font-family: times new roman; font-size: 10pt;"&gt;33,070&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; padding-bottom: 2px; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td align="right" valign="bottom" style="padding-bottom: 2px; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="border-bottom: black 2px solid; text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="border-bottom: black 2px solid; text-align: right; width: 9%; font-family: times new roman; font-size: 10pt;"&gt;33,070&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; padding-bottom: 2px; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="white"&gt;&lt;td align="left" valign="bottom" style="padding-bottom: 4px; width: 76%;"&gt;&lt;div style="text-align: left; text-indent: 0pt; display: block; font-family: times new roman; margin-left: 0pt; font-size: 10pt; margin-right: 0pt;"&gt;Total&lt;/div&gt;&lt;/td&gt;&lt;td align="right" valign="bottom" style="padding-bottom: 4px; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="border-bottom: black 4px double; text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;$&lt;/td&gt;&lt;td valign="bottom" style="border-bottom: black 4px double; text-align: right; width: 9%; font-family: times new roman; font-size: 10pt;"&gt;503,158&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; padding-bottom: 4px; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td align="right" valign="bottom" style="padding-bottom: 4px; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;td valign="bottom" style="border-bottom: black 4px double; text-align: left; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;$&lt;/td&gt;&lt;td valign="bottom" style="border-bottom: black 4px double; text-align: right; width: 9%; font-family: times new roman; font-size: 10pt;"&gt;527,643&lt;/td&gt;&lt;td nowrap="nowrap" valign="bottom" style="text-align: left; padding-bottom: 4px; width: 1%; font-family: times new roman; font-size: 10pt;"&gt;&amp;#160;&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt;&lt;/div&gt;&lt;div style="text-indent: 0pt; display: block;"&gt;&amp;#160;&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>The entire disclosure for inventory. This may include, but is not limited to, the basis of stating inventory, the method of determining inventory cost, the major classes of inventory, and the nature of the cost elements included in inventory. If inventory is stated above cost, accrued net losses on firm purchase commitments for inventory and losses resulting from valuing inventory at the lower-of-cost-or-market may also be included. For LIFO inventory, may disclose the amount and basis for determining the excess of replacement or current cost over stated LIFO value and the effects of a LIFO quantities liquidation that impacts net income.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 210

 -SubTopic 10

 -Section 50

 -Paragraph 1

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 210

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 -Section S99

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

 -Publisher SEC

 -Name Regulation S-X (SX)

 -Number 210

 -Section 02

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