<PAGE>

                                                                    Exhibit 10.1

                      EIGHTH AMENDMENT TO CREDIT AGREEMENT

     This EIGHTH AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is effective
as of September 29, 2002, and is entered into by and among Opinion Research
Corporation, a Delaware corporation ("Parent"), ORC INC., a Delaware corporation
("ORC", Parent and ORC are sometimes collectively referred to herein as the
"Borrowers" and individually as a "Borrower"), the Subsidiaries of Borrowers
party hereto, Heller Financial, Inc., in its capacity as Agent for the Lenders
party to the Credit Agreement described below ("Agent"), and the Lenders which
are signatories hereto.

     WHEREAS, Agent, Lenders and Borrowers are parties to a certain Credit
Agreement dated as of May 26, 1999 (as such agreement has from time to time been
amended, supplemented or otherwise modified, the "Agreement"); and

     WHEREAS, the parties desire to amend the Agreement as hereinafter set
forth.

     NOW, THEREFORE, in consideration of the mutual conditions and agreements
set forth in the Agreement and in this Amendment, and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto hereby agree as follows:

     1. Definitions. Capitalized terms used in this Amendment, unless otherwise
defined herein, shall have the meaning ascribed to such terms in the Agreement.

     2. Amendments. Subject to the conditions set forth below, the Agreement is
amended as follows:

     (a) Section 1.1(B)(1) of the Credit Agreement is amended by deleting the
first sentence and substituting the following therefor:

         (B) Revolving Loans. (1) Each Lender agrees, severally and not jointly,
     to lend to Borrowers from the Closing Date to the Expiry Date its Pro Rata
     Share of the loans requested by Parent, on behalf of Borrowers, to be made
     by Lenders under this subsection 1.1(B), up to an aggregate maximum for all
     Lenders of (i) $24,000,000 until the Eighth Amendment Effective Date and
     (ii) $19,000,000 on and after the Eighth Amendment Effective Date (as the
     same may be reduced and otherwise in effect from time to time hereunder,
     the "Revolving Loan Commitment").

     (b) In furtherance of the provisions of Section 2(a) above, the Lenders,
Agent and Borrowers hereby agree that each Lender's commitment to make Revolving
Loans shall be amended and restated, effective as of the Eighth Amendment
Effective Date, as set forth on Schedule 1 hereto. The Lenders, Agent and
Borrowers hereby agree that the defined term "Pro

                                        1

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Rata Share" set forth in Section 10.1 of the Credit Agreement shall be deemed to
be amended in all relevant respects to give effect to the terms of the preceding
sentence.

     (c) Section 4.3 of the Agreement shall be amended in its entirety and as so
amended shall read as follows:

         "4.3 EBITDA. Borrowers shall not permit EBITDA for any twelve (12)
     month period ending on the date set forth below to be less than the amount
     set forth below for such date.

              Period Ending                               Amount
              -------------                               ------
              June 30, 1999                               $14,000,000
              September 30, 1999                          $14,500,000
              December 31, 1999                           $15,000,000
              March 31, 2000                              $15,000,000
              June 30, 2000                               $15,500,000
              September 30, 2000                          $15,500,000
              December 31, 2000                           $15,750,000
              March 31, 2001                              $15,750,000
              June 30, 2001                               $16,250,000
              September 30, 2001                          $16,250,000
              December 31, 2001                           $17,000,000
              March 31, 2002                              $14,500,000
              June 30, 2002                               $15,000,000
              September 30, 2002                          $15,000,000
              December 31, 2002                           $14,250,000
              March 31, 2003                              $14,500,000
              June 30, 2003                               $17,750,000
              September 30, 2003                          $17,750,000
              December 31, 2003                           $18,750,000
              March 31, 2004                              $18,750,000
              June 30, 2004                               $18,750,000
              September 30, 2004                          $18,750,000
              December 31, 2004                           $19,750,000
              March 31, 2005                              $19,750,000
              May 31, 2005                                $19,750,000

     "EBITDA" will be calculated as illustrated on Exhibit 4.8(C)

     (d) Subsection (B) of Section 4.4 of the Agreement shall be amended in its
entirety and as so amended shall read as follows:

         "(B) Borrowers shall not permit Fixed Charge Coverage for any twelve
     (12) month period ending on the last day of any calendar quarter to be less
     than: (i) 1.05 for each of the calendar quarters ending March 31, 2002,
     June 30, 2002,

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     September 30, 2002, December 31, 2002 and March 31, 2003 and (ii) 1.20 for
     any other calendar quarter."

     (e) Section 10.1 of the Credit Agreement shall be amended by adding thereto
the new defined terms "Eighth Amendment" and "Eighth Amendment Effective Date"
in proper alphabetical order, such definitions to read as follows:

         "Eighth Amendment" means that certain Eighth Amendment to Credit
     Agreement effective as of September 29, 2002 by and among Agent, Lenders
     and Borrowers.

         "Eighth Amendment Effective Date" means, subject to the satisfaction of
     the conditions set forth in the Eighth Amendment, September 29, 2002.

     3.  Additional Covenants. Borrowers hereby covenant and agree as follows:

     (a) In the event that (i) an Event of Default occurs under Section 6.1(A)
or (ii) Borrowers breach any of the financial covenants as set forth in Sections
4.1, 4.3, 4.4, 4.5, 4.6, and 4.7 of the Agreement with respect to any period
ending December 31, 2002 or March 31, 2003, within forty-five (45) days after an
Event of Default occurs under Section 6.1(A) or the financial statements for
such period are required to be delivered pursuant to Section 4.8 of the
Agreement, the Borrower shall:

         (x) engage an investment banker that is mutually acceptable to Agent,
     Requisite Lenders, and Borrowers for the purpose of conducting the sale of
     ORC ProTel, Inc. Within such time period, the Agent, Requisite Lenders, and
     Borrowers shall agree upon a mutually satisfactory timeline for completing
     such sale, including, without limitation, establishing milestone dates for,
     among other things, completing marketing materials, soliciting bids,
     completing due diligence and establishing closing dates; and

         (y) engage a consultant or financial advisor reasonably acceptable to
     Agent (the "Advisor") to, specifically including, without limitation:
     analyze the business and operations of Borrowers and their Subsidiaries,
     identify cost cutting measures, conduct analysis of United States market
     research business, and formulate a plan for effectuating such measures
     (collectively, the "Plan"). Borrowers shall cause the Advisor to prepare
     and issue the Plan and to deliver to Agent and Lenders a copy thereof
     within thirty (30) days after the Advisor is engaged. Promptly thereafter,
     Borrowers, Agent, and Lenders shall meet to review and discuss the Plan,
     after which Borrowers shall promptly and with due diligence implement the
     recommendations set forth in such plan.

     (b) Without limiting the Obligations of the Borrowers under any of the Loan
Documents, the Borrowers reaffirm their obligation to deliver timely Projections
as required under Subsection 4.8(I) of the Agreement. Within thirty (30) days of
delivery of such Projections, Agent, Lenders and Borrower shall meet to review
and discuss such Projections at a mutually agreed upon time and location.

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     4.  Conditions. The effectiveness of this Amendment is subject to the
following conditions precedent:

     (a) Borrowers shall have executed and delivered this Amendment, and such
other documents and instruments as Agent may require shall have been executed
and/or delivered to Agent (including, without limitation, true, complete and
correct copies of fully executed documents amending the Subordinated Loan
Agreement in form and substance acceptable to Agent and Required Lenders);

     (b) All proceedings taken in connection with the transactions contemplated
by this Amendment and all documents, instruments and other legal matters
incident thereto shall be satisfactory to Agent and its legal counsel;

     (c) No Default or Event of Default shall have occurred and be continuing;

     (d) The representations and warranties set forth in Section 5 below are
true, correct and complete; and

     (e) Borrowers shall have paid to Agent a non-refundable amendment fee in
the amount of one-eighth of one percent (0.125%) of the "Aggregate Commitment",
such amendment fee to be shared by the Lenders who have executed this Amendment
pro rata based on each Lender's respective share of the Aggregate Commitment
(for purposes of this clause (e), "Aggregate Commitment" shall mean, with
respect to the Lenders who have executed this Amendment, the aggregate Revolving
Loan Commitment of such Lenders plus the outstanding principal amount of Term
Loans of such Lenders, in each case after giving effect to this Amendment and
payment of the Scheduled Installment of the Term Loan on September 30, 2002.)

     5.  Representations and Warranties. To induce Agent and Lenders to enter
into this Amendment, each of the Borrowers represents and warrants to Agent and
Lenders:

     (a) that the execution, delivery and performance of this Amendment has been
duly authorized by all requisite corporate action on the part of such Borrower
and that this Amendment has been duly executed and delivered by such Borrower;
and

     (b) that each of the representations and warranties set forth in the
Agreement and the Subordinated Loan Agreement (in each instance, other than
those which, by their terms, specifically are made as of certain date prior to
the date hereof) are true and correct in all material respects as of the date
hereof

     6.  Severability. Any provision of this Amendment held by a court of
competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

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       7.     References. Any reference to the Agreement contained in any
document, instrument or agreement executed in connection with the Agreement
shall be deemed to be a reference to the Agreement as modified by this
Amendment.

       8.     Counterparts. This Amendment may be executed in one or more
counterparts, each of which shall constitute an original, but all of which taken
together shall be one and the same instrument.

       9.     Ratification. The terms and provisions set forth in this Amendment
shall modify and supersede all inconsistent terms and provisions of the
Agreement and shall not be deemed to be a consent to the modification or waiver
of any other term or condition of the Agreement. Except as expressly modified
and superseded by this Amendment, the terms and provisions of the Agreement are
ratified and confirmed and shall continue in full force and effect.

       10.    Reaffirmation. Each Loan Party party hereto has executed and
delivered one or more of the Security Documents and/or the other Loan Documents
as debtor, grantor, pledgor, guarantor, assignor, or in other similar capacities
in which such Person has granted liens or security interests in their respective
properties or otherwise acted as an accommodation party or guarantor, as the
case may be. Each Loan Party party hereto hereby ratifies and reaffirms all of
its respective payment and performance obligations, contingent or otherwise,
under the Security Documents and any other Loan Documents to which it is a party
and, to the extent any such Person has granted liens on or security interests in
any of their respective properties pursuant to any of the Security Documents or
any of the other Loan Documents as security for or otherwise guaranteed the
Obligations under or with respect to the Agreement or any other Loan Documents,
hereby ratifies and reaffirms such payment and performance obligations,
guarantee and grant of security interests and liens and confirms and agrees that
such security interests and liens hereafter secure all of the Obligations. Each
Loan Party party hereto agrees that each of the Security Documents and each
other Loan Document remains in full force and effect and is hereby ratified and
reaffirmed, and agrees that the Amendment shall not (i) operate as a waiver of
any right, power or remedy of Agent or Lenders under the Loan Documents or (ii)
constitute a waiver of any provision of any of the Loan Documents or serve to
effect a novation of the Obligations.

         [rest of page intentionally left blank; signature page follows]

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       IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed under seal and delivered by their respective duly authorized
officers on the date first written above.

AGENT and LENDERS:                       BORROWERS:

Heller Financial, Inc.,                  OPINION RESEARCH CORPORATION,
as Agent and as a Lender                 a Delaware corporation

By:    /s/ James M. Babcock              By:    /s/ Kevin P. Croke
   ---------------------------------        --------------------------------
Name:  James M. Babcock                  Name:  Kevin P. Croke
     -------------------------------          ------------------------------
Title: Senior Vice President             Title: EVP & Director of Finance
      ------------------------------           -----------------------------

FLEET NATIONAL BANK,                     ORC INC.,
as a Lender                              a Delaware corporation

By:_________________________________     By:    /s/ Kevin P. Croke
                                            --------------------------------
Name:_______________________________     Name:  Kevin P. Croke
                                              ------------------------------
Title:______________________________     Title: President
                                               -----------------------------

WACHOVIA BANK, NATIONAL ASSOCIATION,
as a Lender

By:    /s/ Elizabeth Witherspoon
   ---------------------------------
Name:  Elizabeth Witherspoon
     -------------------------------
Title: Vice President
      ------------------------------

MERRILL LYNCH BUSINESS FINANCIAL SERVICES, INC.,
as a Lender

By:      /s/ Valerie Wilder Moore
   ---------------------------------
Name:    Valerie Wilder Moore
     -------------------------------
Title:   Assistant Vice President
       -----------------------------

PNC BANK, NATIONAL ASSOCIATION,
as a Lender

By:    /s/ Jeffrey A. Blakemore
   ---------------------------------
Name:  Jeffrey A. Blakemore
     -------------------------------
Title: Senior Vice President
      ------------------------------



                       [signatures continued on next page]

<PAGE>

SUBSIDIARIES:

ORC TELESERVICE CORP.,
a Delaware corporation

By:    /s/ Kevin P. Croke
   ---------------------------------
Name:  Kevin P. Croke
     -------------------------------
Title: Secretary
      ------------------------------


ORC PROTEL, INC.,
a Delaware corporation

By:    /s/ Kevin P. Croke
   ---------------------------------
Name:  Kevin P. Croke
     -------------------------------
Title: Secretary
      ------------------------------


MACRO INTERNATIONAL, INC.,
a Delaware corporation

By:    /s/ Kevin P. Croke
   ---------------------------------
Name:  Kevin P. Croke
     -------------------------------
Title: Secretary
      ------------------------------


SOCIAL AND HEALTH SERVICES, LTD.,
a Maryland corporation

By:    /s/ Kevin P. Croke
   ---------------------------------
Name:  Kevin P. Croke
     -------------------------------
Title: Secretary
      ------------------------------