Exhibit 10.2 Letter Agreement


    
      

    

    
      

    

    Exhibit
      10.2 Letter Agreement

     

      [CHEMBIO
        LETTERHEAD]

      


      


      March
        28,
        2006

      


      Mr.
        Robert Hoyt

      Crestview
        Capital Master, LLC

       

      Re: Securities
        Purchase Agreement dated as of January 26, 2005 among Chembio Diagnostics,
        Inc.
        (“Chembio”), Crestview Capital Master, LLC (“Crestview”), and other purchasers
        (the “Agreement”)

      


      Dear
        Bob:

       

      The
        purpose of this letter is to confirm our understandings regarding the purchase
        by Crestview of additional securities of Chembio pursuant to the Agreement.
        Capitalized terms in this letter that are not otherwise defined herein have
        the
        same meanings given to such terms in the Agreement. A First Closing was held
        in
        2005 in which Crestview purchased $3,000,000 of Preferred Stock and Warrants.
        Pursuant to Section 2.1(b) of the Agreement, Crestview is obligated to purchase
        an additional $1,000,000 of Preferred Stock and Warrants in a Second Closing
        upon notice from Chembio that Chembio, as of any fiscal quarter of 2005:
        (1)
        achieved at least $5,000,000 in aggregate contract revenues; and (2) has
        annualized growth profits of at least $2,250,000. This will confirm that
        Chembio
        and Crestview have agreed that these conditions have been satisfied and that
        Crestview is aware of the rationale used by Chembio in the calculations as
        set
        forth in Exhibit A.

       

      The
        shares of Common Stock underlying the Preferred Stock and the Warrants to
        be
        issued to you in connection with this transaction are entitled to registration
        rights pursuant to a Registration Rights Agreement entered into in connection
        with the Agreement. In connection with this Second Closing, and in order
        to
        avoid a costly and detrimental expense at this time, we ask that you waive
        all
        registration rights relating to the securities purchased in this Second Closing.
        We plan to complete a new round of financing within the next few months,
        and we
        will include (piggyback) the resale of the Common Stock underlying the Preferred
        Stock and Warrants purchased by you in the Second Closing in our next
        registration statement. 

       

      In
        connection with this Second Closing, you also confirm that Crestview has
        had the
        opportunity to: (i) discuss Chembio’s business, management and financial affairs
        with management of Chembio; (2) ask questions of, and receive answers from,
        management of Chembio regarding the terms and conditions of this investment;
        and
        (3) review all reports filed by Chembio with the SEC since January
        2005.

       

      We
        also
        appreciate your agreement to close this transaction on March 29, 2006. Upon
        receipt of a signed copy of this letter from Crestview and a wire payment
        to us
        in the amount of $1,000,000 (wire instructions are attached in Schedule A),
        we
        will cause to be registered in the name of Crestview and delivered to Crestview:
        (1) a stock certificate representing 20 shares of Preferred Stock, and (2)
        a
        warrant certificate in the form set forth in the Agreement, representing
        a
        warrant to purchase 1,557,377 shares of Common Stock at an exercise price
        of
        $.61 per share for a period of five years. 

       

      Should
        you have any questions regarding this matter, please contact us. We appreciate
        your cooperation in promptly completing this transaction.

       

      


      Very
        Truly Yours,

      


      CHEMBIO
        DIAGNOSTICS, INC.

      


      By:__________________________

      Richard
        J. Larkin, Chief Financial Officer

      


      


      AGREED
        AND ACKNOWLEDGED:

      


      CRESTVIEW
        CAPITAL MASTER, LLC

      


      By:_______________________________

      Robert
        Hoyt, Authorized Signatory

      


      Dated
        as
        of March 28, 2006