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                                                                   EXHIBIT 4.12

                          FOURTH SUPPLEMENTAL INDENTURE

        FOURTH SUPPLEMENTAL INDENTURE dated as of August __, 1997, among
ENVIROTEST SYSTEMS CORP., a Delaware corporation (the "Company"), ENVIROTEST
TECHNOLOGIES, INC., a Delaware corporation, REMOTE SENSING TECHNOLOGIES, INC., a
Delaware corporation, ENVIROTEST PARTNERS, a Pennsylvania partnership,
ENVIROTEST ACQUISITION CO., a Delaware corporation, SYSTEMS CONTROL, INC., a
Washington corporation, and ENVIROTEST ILLINOIS, INC., a Delaware corporation
(the "Guarantors"), and FIRST TRUST NATIONAL ASSOCIATION, as Trustee (the
"Trustee").

                                    RECITALS

        WHEREAS, the Company, the Guarantors and the Trustee entered into an
Indenture, dated as of March 15, 1994 (the "Original Indenture"), pursuant to
which the Company issued $200,000,000 in principal amount of its 9 1/8% Senior
Notes due 2001 (the "Securities") (capitalized terms used herein without
definition shall have the respective meanings ascribed to them in the
Indenture); and

        WHEREAS, the Company, the Guarantors named therein and the Trustee
amended the Original Indenture by entering into a First Supplemental Indenture
dated as of May 28, 1994 (the "First Supplemental Indenture") in accordance with
Section 9.1 of the Original Indenture; and

        WHEREAS, the Company, the Guarantors named therein and the Trustee
amended the Original Indenture and the First Supplemental Indenture by entering
into a Second Supplemental Indenture dated as of January 30, 1996 (the "Second
Supplemental Indenture") in accordance with Section 9.1 of the Original
Indenture; and

        WHEREAS, the Company, the Guarantors named therein and the Trustee
amended the Original Indenture, the First Supplemental Indenture and the Second
Supplemental Indenture by entering into a Third Supplemental Indenture dated as
of March 25, 1997 (the "Third Supplemental Indenture") in accordance with
Section 9.1 of the Original Indenture (as so supplemented and amended by the
First Supplemental Indenture, the Second Supplemental Indenture and the Third
Supplemental Indenture, the "Indenture"); and

        WHEREAS, Section 9.2 of the Indenture provides that the Company, the
Guarantors and the Trustee may amend or supplement the Indenture with the
written consent of the Holder or Holders of at least a majority in aggregate
principal amount of the outstanding Securities; and

        WHEREAS, all acts and things prescribed by the Indenture, by law and by
the Restated Certificate of Incorporation and the Second Amended and Restated
Bylaws of










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the Company, of the Guarantors and of the Trustee necessary to make this Fourth
Supplemental Indenture a valid instrument legally binding on the Company, the
Guarantors and the Trustee, in accordance with its terms, have been duly done
and performed; and

        WHEREAS, the written consent to the amendments or supplements to the
Indenture have been obtained from not less than a majority of the Holders in the
aggregate principle amount of the outstanding Securities; and

        WHEREAS, all condition precedent to amend or supplement the Indenture
have been met;

        NOW, THEREFORE, to comply with the provisions of the Indenture, and in
consideration of the above premises, the Company, the Guarantors, and the
Trustee covenant and agree to the equal and proportionate benefit of the
respective Holders of the Securities as follows:

                                    ARTICLE 1

        Section 1.01. This Fourth Supplemental Indenture is supplemental to the
Indenture and does and shall be deemed to form a part of, and shall be construed
in connection with and as part of, the Indenture for any and all purposes,
including but not limited to discharge of the Indenture as provided in Article 8
of the Indenture.

        Section 1.02. Definitional Amendments.

a.      ab.    Section 1.1 of the Indenture is hereby amended by deleting the
               word "and" appearing before "(vi)" in the definition of
               "Permitted Investment".

        b.     abSection 1.1 of the Indenture is hereby amended by adding a new
               section to the end of the definition of "Permitted Investment"
               which reads in its entirety:

               and (vii) on and after the initial Consent Payment Obligation
               Date, Investments by the Company or any of its Subsidiaries not
               to exceed (together with Restricted Payments made pursuant to the
               third paragraph of Section 4.3) $10.0 million in the aggregate;
               provided, however, that such amount may be increased, at the
               election of the Company, which election may be made at any time
               prior to September 30, 1997, up to $20.0 million (which election
               may be made in one or two equal $5.0 million installments) if for
               each increase of $5.0 million the Company agrees to pay to the
               Consenting Holders an amount equal to .5% of the principal amount
               of Notes to which such Holder's consent relates.








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c.     ab      Section 1.1 of the Indenture is hereby amended by deleting the
               word "or" appearing before the "(iv)" in the definition of
               Restricted Payment.

d.     ab      Section 1.1 of the Indenture is hereby amended by adding a new
               section to the end of the definition of "Restricted Payment"
               which reads in its entirety:

               ,or (v) any payment to the holders of Senior Subordinated Notes
               in respect of the consent solicitation of such holders being
               effected pursuant to the Company's Consent Solicitation Statement
               dated August 4, 1997 (as supplemented on August 8, 1997).

e.     ab.     Section 1.1 of the Indenture is amended to include the following
               definitions:

               "9 1/8% Notes Offer" means an offer (which offer may contain
               conditions (other than with respect to any buy back of any of the
               Company's outstanding equity securities) customarily contained in
               debt tender offers) by the Company to the holders of the Notes to
               purchase up to $50 million aggregate principal amount of Notes at
               a price of 100% plus accrued and unpaid interest or pursuant to a
               "Dutch Auction" tender offer with a top range of 100% plus
               accrued and unpaid interest.

               "Consenting Holder" shall mean the holder of the Notes who duly
               consented to the Proposed Amendments set forth in the Company's
               Consent Solicitation Statement dated August 4, 1997 (as
               supplemented on August 8, 1997). 

               "Consent Payment" means, the Initial Payment and, for each Option
               Increase, the Optional Increase Payment, if applicable.

               "Consent Payment Date" means the earlier of (i) five Business
               Days after the expiration of the 9 1/8% Notes Offer and (ii)
               September 30, 1997.

               "Consent Payment Obligation Date", means the date the 9 1/8%
               Notes Offer expires; provided that on or after such date the
               Company accepts (subject to the terms and conditions of such
               offer) securities validly tendered pursuant to and in accordance
               with the terms of such offer.

               "Initial Payment" means, for each Consenting Holder who duly
               consented to the Proposed Amendments set forth in the Company's
               Consent Solicitation Statement dated August 4, 1997 (as
               supplemented on August 8, 1997), 1.0% of the principal amount of
               Securities to which such Consenting Holder's consent relates.

               "Optional Increase" shall mean the exercise by the Company of its









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               election to increase the amount of Investments permitted to be
               made by subsection (vii) of the definition of Permitted
               Investments and the amount of Restricted Payments permitted to be
               made by the third paragraph of Section 4.3.

               "Optional Increase Payment" shall mean the amount required to be
               paid to Consenting Holders as a consequence of the exercise by
               the Company of any Optional Increase.

        Section 1.03. Amendments to Article IV.

        a.     A  new paragraph is added to the end of Section 4.3 which reads
               in its entirety:

                      Notwithstanding anything herein to the contrary, on and
               after the initial Consent Payment Obligation Date the provisions
               of this Indenture will not prohibit or restrict in any way the
               Company or any of its Subsidiaries from making other Restricted
               Payments not to exceed (together with Permitted Investments made
               pursuant to subsection (vii) of the definition of Permitted
               Investments) $10.0 million in the aggregate; provided, however,
               that such amount may be increased, at the election of the
               Company, which election may be made at any time prior to
               September 30, 1997, up to $20.0 million (which election may be
               made in one or two equal $5.0 million installments) if for each
               increase of $5.0 million the Company agrees to pay to the
               Consenting Holders an amount equal to .5% of the principal amount
               of Notes to which such Holder's consent relates. The payment of
               each Restricted Payment paid in accordance with this paragraph
               shall be counted for purposes of computing amounts expended
               pursuant to clause (c) of the first paragraph of this Section
               4.3.

        Section 1.04. Addition of New Section.

        a.     A Section 13.16 is added which reads in its entirety:

               SECTION 13.16 Consent Payments.

                      On or prior to a Consent Payment Date, the Company shall
               deposit with the Paying Agent (other than the Company, a
               Guarantor or an Affiliate of the Company or Guarantor) U.S. Legal
               Tender sufficient to pay the Initial Payment or the Optional
               Increase Payment, as applicable, to all Consenting Holders, and
               upon such payment the Company shall be deemed for all purposes
               hereunder to have made such Consent Payments to the Consenting
               Holders. If the Consent Payment Date is a Legal Holiday, payment
               shall be made on the next succeeding







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               Business Day and no interest shall accrue for the period from
               such Consent Payment Date to such succeeding Business Day. Any
               Consent Payment shall be paid to each Consenting Holder
               notwithstanding that such Consenting Holder is no longer the
               registered owner on the Consent Payment Date of the Securities to
               which such Consenting Holder's consent related. The Paying Agent
               shall promptly return to the Company any U.S. Legal Tender so
               deposited which is not required for that purpose upon the written
               request of the Company.

                      In addition, on or prior to a Consent Payment Date, the
               Company shall mail a notice by first class mail, postage prepaid,
               to the Trustee and each Consenting Holder. At the Company's
               request, the Trustee shall give such notice in the Company's name
               and at the Company's expense. Each such notice shall state: (i)
               the Consent Payment Date; (ii) the number of Optional Increases
               exercised, if applicable; (iii) the amount of the Consent
               Payment; (iv) the name, address and telephone number of the
               Paying Agent; (iv) the CUSIP number of the Securities to which
               the Consent Payment relates; and (v) that the notice is being
               sent pursuant to this Section 13.16.

                                    ARTICLE 2

        Section 2.01. Except as specifically modified herein, the Indenture and
the Securities are in all respects ratified and confirmed and shall remain in
full force and effect in accordance with their terms.

        Section 2.02. Except as otherwise expressly provided herein, no duties,
responsibilities or liabilities are assumed or shall be construed to be assumed,
by the Trustee by reason of this Fourth Supplemental Indenture. This Fourth
Supplemental Indenture is executed and accepted by the Trustee subject to all
the terms and conditions set forth in the Indenture with the same force and
effect as if those terms and conditions were repeated at length herein and made
applicable to the Trustee with respect hereto.

        Section 2.03. The laws of the State of New York shall govern this Fourth
Supplemental Indenture without regard to principles of conflicts of law. The
Trustee, the Company and the Guarantors agree to submit to the jurisdiction of
the courts of the State of New York in any action or proceeding arising out of
or relating to this Fourth Supplemental Indenture.

        Section 2.04. The parties may sign any number of copies of this Fourth
Supplemental Indenture. Each signed copy shall be an original, but all of such
executed copies together shall represent the same agreement.


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                                   SIGNATURES

        IN WITNESS WHEREOF, the parties hereto have caused this Fourth
Supplemental Indenture to be duly executed, all as of the date first written
above.

                                     COMPANY

                                     ENVIROTEST SYSTEMS CORP.


                                     By: /s/ F. Robert Miller
                                        ---------------------------------
                                        Name:  F. Robert Miller
                                        Title: CEO


                                     GUARANTORS

                                     ENVIROTEST TECHNOLOGIES, INC.


                                     By: /s/ F. Robert Miller
                                        ---------------------------------
                                        Name:  F. Robert Miller
                                        Title: CEO


                                     ENVIROTEST PARTNERS

                                     By:  ENVIROTEST SYSTEMS CORP.,
                                          its general partner


                                     By: /s/ F. Robert Miller
                                        ---------------------------------
                                        Name:  F. Robert Miller
                                        Title: CEO


                                     REMOTE SENSING TECHNOLOGIES, INC.


                                     By: /s/ F. Robert Miller
                                        ---------------------------------
                                        Name:  F. Robert Miller
                                        Title: CEO


                                     ENVIROTEST ACQUISITION CO.


                                     By: /s/ F. Robert Miller
                                        ---------------------------------
                                        Name:  F. Robert Miller
                                        Title: CEO




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                                     SYSTEMS CONTROL, INC.


                                     By: /s/ F. Robert Miller
                                        ---------------------------------
                                        Name:  F. Robert Miller
                                        Title: CEO


                                     ENVIROTEST ILLINOIS, INC.


                                     By: /s/ F. Robert Miller
                                        ---------------------------------
                                        Name:  F. Robert Miller
                                        Title: CEO

[Seal]

Attest:_________________


                                     FIRST TRUST NATIONAL
                                     ASSOCIATION, as Trustee



                                     By: /s/ Richard H. Prokosch
                                        ---------------------------------
                                        Name:  Richard H. Prokosch
                                        Title:


Attest: /s/ K. Banett
       -----------------------