SECOND SUPPLEMENTAL INDENTURE, dated as of October 1, 1996 between
MEDIQ/PRN Life Support Services, Inc., a Delaware corporation (the "Company"),
and Summit Bank f/k/a United Jersey Bank, as Trustee (the "Trustee") under that
certain Indenture dated as of July 6, 1992 as supplemented by Supplemental
Indenture dated as of September 30, 1994 (as so supplemented, the "Indenture").

                             W I T N E S S E T H:

      WHEREAS, the Company has heretofore executed and delivered to the Trustee
the Indenture providing for the issuance of the Company's 11-1/8% Senior Secured
Notes Due 1999 (the "Senior Secured Notes"); and

      WHEREAS, Section 9.02 of the Indenture authorizes the Company and the
Trustee, with the consent of at least a majority in aggregate principal amount
of the Senior Secured Notes then Outstanding, to amend the Indenture, the
Security Documents or the Senior Secured Notes and to execute a Supplemental
Indenture in connection therewith, to make certain changes; and

      WHEREAS, all acts and proceedings required by law and by the Indenture to
constitute this Supplemental Indenture a valid and binding agreement for the
uses and purposes herein as set forth, in accordance with its terms, have been
done and taken, and the execution and delivery of this Second Supplemental
Indenture have been in all respects duly authorized by the Company.

      NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt of which is hereby acknowledged, each party
hereto covenants and agrees with the other party, for the equal and
proportionate benefit of all present and future Noteholders, as follows:

            1. The Indenture is hereby amended by deleting the following
Sections in their entirety:

            (a)   4.03

            (b)   4.04

            (c)   4.05

            (d)   4.09

            (e)   4.10

            (f)   4.14


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            (g)   4.15

            (h)   4.18

            2. The definition of "Permitted Liens" is hereby amended by adding
two new clauses (xii) and (xiii) at the end of such definition as follows:

            "and (xii) Liens on any assets which are not subject to the Liens of
      the Trustee for the benefit of the Noteholders, and (xiii) Liens on assets
      subject to the Liens of the Trustee for the benefit of Noteholders, but
      which are expressly subordinate in priority to such Liens in favor of the
      Trustee created under this Indenture."

            3.    Section 2.09 of the Indenture is hereby amended by
deleting such Section in its entirety and replacing it with the
following:

      "Section 2.09.  Outstanding Senior Secured Notes.

            Senior Secured Notes outstanding at any time are all Senior Secured
      Notes that have been authenticated by the Trustee, except for those
      cancelled or deemed cancelled pursuant to Section 2.12(b) hereof by the
      Trustee, those delivered to it for cancellation and those described in
      this Section as not outstanding. A Senior Secured Note does not cease to
      be outstanding because the Company or one of its Affiliates holds the
      Senior Secured Note.

            If a Senior Secured Note is replaced pursuant to Section 2.08, it
      ceases to be outstanding unless the Trustee receives proof satisfactory to
      it that the replaced Senior Secured Note is held by a bona fide purchaser.

            If the Paying Agent (other than the Company or a Subsidiary of the
      Company) holds, on a redemption date or the Maturity Date, money
      sufficient to pay all accrued interest and principal with respect to such
      Senior Secured Notes payable on that date and is not prohibited from
      paying such money to the Holders thereof pursuant to the terms of this
      Indenture, then on and after that date such Senior Secured Notes cease to
      be outstanding and interest on them cease to accrue."

            4.    Section 2.12 of the Indenture is hereby amended by
designating the existing text as subsection "(a)" and adding a
new subsection (b) as follows:

            "(b) In the event that the Company deposits trust monies with the
            Trustee pursuant to Section 8.01(a)(ii) hereof and the Company or an
            Affiliate of the Company


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<PAGE>

            holds Senior Secured Notes for which no such deposit is being made,
            all such Senior Secured Notes held by the Company or its Affiliate
            shall be deemed cancelled by the Trustee pursuant to this Section
            2.12 effective immediately prior to the Trustee's receipt of such
            deposit, regardless of whether such Senior Secured Notes have been
            delivered to the Trustee in accordance with Section 2.12(a)."

            5.    Section 4.13(b) is hereby amended by deleting such
Section and replacing it with the following:

            "(b) requires, prior to the payment in full or defeasance of the
      Senior Secured Notes, that the proceeds received from the sale of any
      Collateral be applied to repay, redeem or otherwise retire any
      Indebtedness of any Person other than the Indebtedness represented by the
      Senior Secured Notes."

            6. Section 4.17 is hereby amended by adding the following sentence
to the end of such Section:

            "Notwithstanding anything to the contrary contained herein, the
      Company and its subsidiaries and Affiliates may grant Liens on any assets
      which are not subject to the Liens of the Trustee for the benefit of the
      Noteholders."

            7. Section 5.01 of the Indenture is hereby amended by deleting
Subsection 5.01(ii) in its entirety and renumbering existing Subsection
5.01(iii) as 5.01(ii).

            8. Section 8.01 of the Indenture is hereby amended by deleting such
Section in its entirety and by replacing such Section with the following:

      "SECTION 8.01.  Termination of Obligations.

            The Company may terminate its obligations under the Senior Secured
      Notes and this Indenture, except those obligations referred to in the
      immediately succeeding paragraph, if:

            (a) (i) all Senior Secured Notes previously authenticated and
      delivered (other than destroyed, lost or stolen Senior Secured Notes which
      have been replaced or paid) have been delivered to the Trustee for
      cancellation or have been deemed cancelled pursuant to Section 2.12(b)
      hereof or monies sufficient for the payment of Senior Secured Notes which
      are due and payable but have not been surrendered for payment shall have
      been deposited with the Trustee or Paying Agent and the Company has paid
      all sums payable by it hereunder; or


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<PAGE>

            (ii) the Company shall have irrevocably deposited or caused to be
      deposited with the Trustee or the Paying Agent, under the terms of an
      irrevocable trust agreement in form and substance satisfactory to the
      Trustee, as trust funds in trust solely for the benefit of the Holders
      (other than the Company or any Affiliates of the Company) for that
      purpose, money or direct non-callable obligations of, or non-callable
      obligations guaranteed by, the United States of American for the payment
      of which guarantee or obligation the full faith and credit of the United
      States is pledged ("U.S. Government Obligations"), maturing as to
      principal and interest in such amounts and at such times as are
      sufficient, without consideration of any reinvestment of such interest, to
      pay principal of and interest on the outstanding Senior Secured Notes held
      by Holders other than the Company or any Affiliate to maturity or
      redemption, as the case may be, as certified by the Company in an
      Officers' Certificate; provided that the Trustee shall have been
      irrevocably instructed pursuant to such Officers' Certificate to apply
      such money or the proceeds of such U.S. Government Obligations to the
      payment of said principal and interest with respect to the Senior Secured
      Notes held by Holders other than the Company or any Affiliate of the
      Company; and provided, further, that the Company shall have delivered to
      the Trustee an Opinion of Counsel to the effect that, after the passage of
      124 days following the deposit, the trust funds will not be subject to the
      effect of any applicable bankruptcy, insolvency, reorganization or similar
      laws affecting creditors' rights generally; and

            (b) the Company pays or causes to be paid all other sums then
      payable by the Company hereunder; or

            (c) the Company delivers to the Trustee an Officers' Certificate and
      an Opinion of Counsel, each stating that all conditions precedent provided
      for herein relating to this satisfaction and discharge of this Indenture
      have been complied with;

      provided, however, that no deposit under 8.01(a)(ii) shall be effective to
      terminate the obligations of the Company under the Senior Secured Notes or
      this Indenture prior to 124 days following such deposit.

            Notwithstanding the foregoing paragraph, the Company's obligations
      in Sections 2.03, 2.04, 2.05, 2.06, 2.07, 2.13, 4.02, 7.07, 7.08, 8.03 and
      8.04 shall survive until the Senior Secured Notes are no longer
      outstanding. Thereafter, the Company's obligations in Sections 7.07, 8.03
      and 8.04 shall survive.


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<PAGE>

            After such delivery or irrevocable deposit the Trustee upon request
      shall acknowledge in writing the discharge of the Company's obligations
      under the Senior Secured Notes and this Indenture except for those
      surviving obligations specified above.

            The Company will pay any taxes or other expenses incurred by any
      trust created pursuant to this Article 8."

            9. Section 8.02 of the Indenture is hereby amended by deleting such
Section in its entirety and replacing such Section with the following:

      "SECTION 8.02.  Application of Trust Money

            "The Trustee or Paying Agent shall hold in trust money or U.S.
      Government Obligations deposited with it pursuant to Section 8.01, and
      shall apply the deposited money and the money from U.S. Government
      Obligations in accordance with this Indenture to the payment of principal
      of and interest on the Senior Secured Notes; provided, however, that
      notwithstanding to anything the contrary contained herein the Trustee
      shall have no obligation to make payments of principal and interest under
      this Indenture for Senior Secured Notes held by the Company or its
      Affiliates for which no deposit was made under Section 8.01 hereof. The
      Trustee shall be under no obligation to invest said money or U.S.
      Government Obligations except as it may agree with the Company."

            10. Except as expressly amended, the Indenture and the Senior
Secured Notes issued thereunder are in all respects ratified and confirmed and
all the terms, conditions and provisions shall remain in full force and effect.
Capitalized terms used herein but not defined shall have the meanings given to
such terms in the Indenture.

            11. This Second Supplemental Indenture shall form a part of the
Indenture for all purposes, and every Note heretofore or hereafter authenticated
and delivered shall be bound hereby.

            12. This Second Supplemental Indenture may be executed in any number
of counterparts, each of which when so executed shall be deemed to be an
original, and all of such counterparts together constitute one and the same
instrument. All capitalized terms used and not otherwise defined herein shall
have the meanings given to them in the Original Indenture, the Senior Secured
Notes or the Security Documents as applicable.

            13. This Second Supplemental Indenture shall be construed in
accordance with and governed by the laws of the State of New Jersey.


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      IN WITNESS WHEREOF, the parties hereto have caused this Second
Supplemental Indenture to be duly executed, and their respective seals to be
hereunto affixed and attested, all as of the day and year first above written.

[Corporate Seal]                    MEDIQ/PRN Life Support Services, Inc.


                                    By  /s/ Jay M. Kaplan
                                      -------------------------------

                                    Attest: /s/ Alan Einhorn
                                           --------------------------

[Corporate Seal]                    Summit Bank f/k/a United Jersey Bank,
                                      as Trustee


                                    By  /s/ Donna J. Flanagan
                                      -------------------------------

                                    Attest:__________________________


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