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                                                                   EXHIBIT 10.21


                                                                     Porter Lane






                                December 1, 2000



Mr. Richard A. Parlontieri
Emissions Testing, Inc.
400 Colony Park
Building 104, Suite 600
Cumming, Georgia  30041

          Re:  Letter Agreement Regarding 210,000 Shares of the Common Stock of
               Emissions Testing, Inc., a Georgia Corporation (the "Company"),
               Owned of Record by Porter Lane Investments, Inc. ("Porter Lane")

Dear Mr. Parlontieri:

     As you know, Porter Lane is the owner of record of 210,000 shares of the
common stock, no par value per share, of the Company.

     The Company has filed a registration statement on Form S-1 (the
"Registration Statement") with the Securities and Exchange Commission (the
"SEC") for the registration of certain shares of the Company's common stock
("Common Stock"), in a public offering (the "Offering") under the Securities Act
of 1933, as amended (the "Act"). Among the shares of Common Stock to be
registered in the Offering are 100,000 shares of Common Stock owned of record by
Porter Lane ( the "Registered Shares"). The balance of the shares of Common
Stock owned by Porter Lane, I.E., 110,000 shares, will not be registered with
the SEC by the Company in the Offering (the "Restricted Shares").

     Inasmuch as Porter Lane wishes to induce the Company to continue its
efforts in connection with the Offering, Porter Lane hereby agrees with, and
represents to, the Company that Porter Lane will not, directly or indirectly,
sell, offer to sell, grant an option for the sale of, assign, transfer, pledge,
hypothecate or otherwise encumber or dispose of in any manner, any of the
Registered Shares (or any interest therein) or any of the Restricted Shares (or
any interest therein), INCLUDING, WITHOUT LIMITATION, PURSUANT TO RULE 144 OR
RULE 144A UNDER THE ACT, from and after the date hereof except as follows:

          (a)  The Company agrees that Porter Lane shall have the right to sell,
               offer to sell, grant an option for the sale of, assign, transfer,
               pledge, hypothecate or otherwise encumber and/or dispose of in
               any manner, up to and including

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Emissions Testing, Inc.
December 1, 2000
Page 2


               50,000 of the Registered Shares at any time after the moment that
               the SEC declares the Registration Statement effective under the
               Act (the "Effective Date"); and

          (b)  The Company further agrees that Porter Lane shall have the right
               to sell, offer to sell, grant an option for the sale of, assign,
               transfer, pledge, hypothecate or otherwise encumber and/or
               dispose of in any manner, all or any part of the Registered
               Shares and all or any part of the Restricted Shares at any time
               after the earlier of (I) 12:01 AM (Atlanta, Georgia time) on
               October 1, 2001, or (II) the date and time that the Company has
               reduced to $250,000 or below the outstanding aggregate principal
               amount of the Company's indebtedness to GCA Strategic Investment
               Fund Limited, a Bermuda corporation ("GCA") (or its assignees)
               under the convertible debentures issued and sold (before or after
               the date hereof) by the Company pursuant to the terms of that
               certain Securities Purchase Agreement dated effective as of June
               1, 2000 between the Company and GCA, as the same may be amended
               from time to time.

     Porter Lane agrees and understands that:

          (c)  Any sale or other transaction involving all or any part of
               Registered Shares and all or any part of the Restricted Shares
               are, and shall hereafter remain, subject to all applicable
               federal and state securities laws and regulations.

          (d)  The Company may place a legend reflecting this letter and terms
               hereof on any certificate evidencing all or any part of the
               shares described herein, and may give written notice of this
               letter, and the terms hereof, to the Company's transfer agent;

          (e)  This letter, and the terms hereof, shall be binding upon Porter
               Lane and the successors and assigns of Porter Lane; and

          (f)  The Company is relying upon the agreements and representations of
               Porter Lane set forth in this letter in filing the Registration
               Statement and amendments thereto and in consummating the
               Offering.

     The Company agrees that, upon the occurrence of the event described in
subparagraph (b) (II) above, the Company shall give prompt written notice
thereof to Porter Lane at the last known address then available to the Company.

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Emissions Testing, Inc.
December 1, 2000
Page 3



         The parties hereto agree that this Letter Agreement shall not be
amended, modified or terminated without the prior written consent of GCA, which
consent may be granted or denied in the sole discretion of GCA.

         If the foregoing meets with your understanding of our agreement, please
so signify by signing and returning this Letter Agreement to us.

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<S>                                   <C>
                                      Very truly yours,

                                      PORTER LANE INVESTMENTS, INC.


                                      By: /s/ Gerald F. Sullivan
                                          --------------------------------
                                        Name: Gerald F. Sullivan
                                             -----------------------------
                                         Position: President
                                                  ------------------------
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Agreed to and accepted as of the
day and year first above written.


EMISSIONS TESTING, INC.


By: /s/ Rich Parlontieri
    ------------------------------
   Name: Rich Parlontieri
         -------------------------
   Position: President/CEO
            ----------------------