Exhibit 10.38


                              MKS INSTRUMENTS, INC.

                                 NINTH AMENDMENT

                                TO LOAN AGREEMENT


         This Ninth Amendment (the "Amendment") dated as of July 31, 2001
concerns the Loan Agreement dated as of October 31, 1995 (the "Loan Agreement"),
between MKS Instruments, Inc. (the "Borrower") and Fleet National Bank (f/k/a
BankBoston, N.A. and The First National Bank of Boston, the "Lender"), as
amended on February 23, 1996, February 4, 1997, February 3, 1998, January 28,
1999, January 1, 2000, September 1, 2000, January 1, 2001 and April 30, 2001.
Capitalized terms used herein but not otherwise defined shall have the meanings
assigned to them in the Loan Agreement.

         WHEREAS, the Loan Agreement was previously amended to provide for terms
consistent with those set forth in the First Amended and Restated Loan Agreement
among the Borrower, the Lender and The Chase Manhattan Bank, which is now being
replaced by a new Credit Agreement (the "Credit Agreement"); and

         WHEREAS, the Lender and the Borrower are willing to amend the Loan
Agreement to make its terms consistent with the terms in the Credit Agreement;

         NOW, THEREFORE, the Lender and the Borrower agree as follows:

         Section 1. Amendment of the Loan Agreement.

         (A) Article I of the Loan Agreement is hereby amended by the deletion
of all subsection numbers at the beginnings of the definitions, the deletion of
the definitions of "Base Rate", "Cash Flow Ratio", "Consolidated Debt Service",
"Debt-to-New Worth Ratio", "Indebtedness", and "Sub S Dividends", and the
addition of the following definitions in alphabetical order:

                   "Accounts" shall mean, at any time, all accounts receivable
          of Borrower and its subsidiaries on a consolidated basis determined in
          accordance with GAAP appearing on the Borrower's consolidated balance
          sheet.

                   "Adjustment Date" shall mean the first day of the month
          immediately following the month in which a Compliance Certificate is
          to be delivered by the Borrower pursuant to Section 6.1(c).

                   "Applicable Margin" shall mean for each period commencing on
          an Adjustment Date through the date immediately preceding the next
          Adjustment Date, the applicable margin set forth below with respect to
          the Debt-To-Tangible Net Worth Ratio, as determined for the most
          recent fiscal quarter for which the Borrower has delivered its
          financial statements pursuant to Section 6.1(a) or (b) and Compliance
          Certificate pursuant to Section 6.1(c):



                           DEBT-TO-TANGIBLE             APPLICABLE MARGIN
                            NET WORTH RATIO              FOR LIBOR LOANS
                                                     
                       Greater than or equal to               2.00%
                       0.50:1.00

                       Less than 0.50:1.00 but                1.50%
                       greater than or equal to
                       0.25:1.00

                       Less than 0.25:1.00                    1.25%


                   "Base Rate" shall mean the higher of (a) the annual rate of
          interest announced from time to time by Lender at Lender's office at
          100 Federal Street, Boston, Massachusetts, as its "base rate" or (b)
          one-half of one percent (1/2%) above the Federal Funds Effective Rate.
          For the purposes of this definition, "Federal Funds Effective Rate"
          shall mean, for any day, the rate per annum equal to the weighted
          average of the rates on overnight federal funds transactions with
          members of the Federal Reserve System arranged by federal funds
          brokers, as published for such day (or, if such day is not a Business
          Day, for the next preceding Business Day) by the Federal Reserve Bank
          of New York, or if such rate is not so published for any day that is a
          Business Day, the average of the quotations for such day on such
          transactions received by the Lender from three funds brokers of
          recognized standing selected by the Lender.

                  "Change in Control" shall be deemed to have occurred at such
          time after the date hereof that any person (other than, in the case of
          clause (ii) below, John R. Bertucci, together with its affiliates and
          associates (as defined in Rule 12b-2 under the Securities Exchange Act
          of 1934 (the "Exchange Act") or any successor rule thereto):

                           (i) shall file with the Securities and Exchange
                  Commission and deliver to the Borrower a report under or in
                  response to Schedule 13D or 14D-1 (or any successor schedule,
                  form or report) pursuant to the Exchange Act disclosing that
                  such person has become the beneficial owner (as defined in
                  Rule 13D-3 under the Exchange Act, or any successor
                  provisions) of more than 25% of the total voting power of all
                  classes of voting stock of the Borrower or


                                      -2-

                           (ii) shall succeed in having a sufficient number of
                  its nominees elected to the board of directors of the Borrower
                  such that such nominees so elected (whether new or continuing
                  as directors) shall constitute a majority of the board of
                  directors of the Borrower.

                  "Consolidated Current Liabilities" shall mean, at any time,
          all current liabilities of Borrower and its subsidiaries on a
          consolidated basis that in accordance with GAAP are properly
          classified as current liabilities plus all other indebtedness for
          borrowed money except such indebtedness that is subordinated to the
          payment of the Obligations pursuant to an agreement in form and
          substance acceptable to the Lender ("Subordinated Debt").

                  "Consolidated Quick Assets" shall mean, at any time, the sum
          of the cash, Accounts, Short Term Investments and Long Term Fixed
          Income Investments of the Borrower and its Subsidiaries, provided the
          sum of Long Term Fixed Income Investments shall not exceed 25% of the
          amount of the Borrower's cash..

                  "Consolidated Total Liabilities" shall mean, at any time, all
          liabilities of the Borrower and its Subsidiaries on a consolidated
          basis that in accordance with GAAP are properly classified as
          liabilities on the Borrowers' consolidated balance sheet plus the sum
          of (i) the face amount of outstanding Letters of Credit, (ii) sales of
          receivables described in clause (f) of the definition of
          "Indebtedness" below and (iii) Synthetic Leases. In computing such
          aggregate liabilities, the "amount" of the liability with respect to
          any such sale of receivables shall be the amount of unrecovered
          capital or principal investment of the purchaser (other than the
          Borrower or any of its wholly-owned Subsidiaries) thereof, excluding
          amounts representative of yield or interest earned on such investment,
          and the "amount" of any Synthetic Lease shall be the stipulated loss
          value, termination value or other equivalent amount.

                  "ERISA" shall have the meaning set forth in Section 4.12.

                  "GAAP" shall mean generally accepted accounting principles.

                  "Indebtedness" shall mean, for any Person,

                           (a) all obligations of any other Person the payment
                  or collection of which such Person has guaranteed (except by
                  reason of endorsement for collection in the ordinary course of
                  business) or in respect of which such Person is liable,
                  contingently or otherwise, including, without limitation,
                  liable by way of agreement to purchase, to provide funds for
                  payment, to supply funds to or otherwise to invest in such
                  other Person, or otherwise to assure a creditor against loss,


                                      -3-

                           (b) all obligations of any other Person for borrowed
                  money or for the deferred purchase price of property or
                  services secured by (or for which the holder of such
                  indebtedness has an existing right, contingent or otherwise,
                  to be secured by) any mortgage, or other encumbrance upon or
                  in property (including, without limitation, accounts and
                  contract rights) owned by such Person, whether or not such
                  Person has assumed or become liable for the payment of such
                  indebtedness or obligations,

                           (c)  Financing Lease Obligations of such Person,

                           (d) every reimbursement obligation of such Person
                  with respect to letters of credit, bankers' acceptances or
                  similar facilities issued for the account of such Person,

                           (e) every obligation of such Person under any
                  Synthetic Lease,

                           (f) all sales by such Person of (i) accounts or
                  general intangibles for money due or to become due, (ii)
                  chattel paper, instruments or documents creating or evidencing
                  a right to payment of money or (iii) other receivables
                  (collectively "receivables"), whether pursuant to a purchase
                  facility or otherwise, other than in connection with the
                  disposition of the business operations of such Person relating
                  thereto or a disposition of defaulted receivables for
                  collection and not as a financing arrangement, and together
                  with any obligation of such Person to pay any discount,
                  interest, fees, indemnities, penalties, recourse, expenses or
                  other amounts in connection therewith,

                           (g) every obligation of such Person to purchase,
                  redeem, retire or otherwise acquire for value any shares of
                  capital stock of any class issued by such Person, any
                  warrants, options or other rights to acquire any such shares,
                  or any rights measured by the value of such shares, warrants,
                  options or other rights, and

                           (h) every obligation of such Person under any forward
                  contract, futures contract, swap, option or other financing
                  agreement or arrangement (including, without limitation, caps,
                  floors, collars and similar agreements), the value of which is
                  dependent upon interest rates, currency exchange rates,
                  commodities or other indices.

                  "Loan Documents" shall mean each of this Agreement, the Note
          and any other document or instrument executed by the Borrower or any
          of its Affiliates in favor of the Lender in connection with the
          transactions contemplated hereby.


                                      -4-

                  "Long Term Fixed Income Investments" shall mean investment
          grade bonds with long-term debt ratings of A- or A3 or higher by at
          least one nationally recognized rating agency and maturities of three
          years or less.

                  "Material Subsidiary" shall mean each domestic Subsidiary of
          the Borrower (other than Massachusetts securities corporations) with
          gross revenues in excess of 5% of the total gross revenues of the
          Borrower and its Subsidiaries, determined on a consolidated basis, or
          assets in excess of 5% of the total assets of Borrower and its
          Subsidiaries, determined on a consolidated basis, in each case as of
          the end of Borrower's last fiscal quarter.

                  "Quick Ratio" shall have the meaning set forth in Section
         7.11.

                  "Short Term Investments" shall mean short term investments as
          determined in accordance with GAAP.

                  "Subordinated Debt" shall have the meaning set forth in the
          definition of Consolidated Current Liabilities set forth above

                  "Synthetic Lease" shall mean any lease that is treated as an
          operating lease under GAAP and as a loan or financing for U.S. income
          tax purposes.

                  "Total Liabilities-to-Tangible Net Worth Ratio" shall have the
          meaning set forth in Section 7.10.

         (B) Section 2.2.1 of the Loan Agreement is hereby deleted in its
entirety and replaced by the following:

                  2.2.1. Borrower agrees to pay interest in respect of the
         unpaid principal amount of the Term Loan from the date of this
         Agreement until paid in full as follows. The Term Loan shall bear
         interest at the Base Rate unless the Borrower desires to pay interest
         on all or a portion of the Term Loan at the LIBOR Rate plus the
         Applicable Margin; provided, however, that the Applicable Margin shall
         not be less than 1.5% prior to the first day of the month following the
         month in which the Borrower shall deliver to the Lender the financial
         statements required by Section 6.1(b) for the year ended December 31,
         2001 and related Compliance Certificate.

          (C) Section 6.1 of the Loan Agreement is hereby deleted in its
entirety and replaced by the following:

                  6.1 Reporting Requirements. The Borrower shall furnish to the
         Lender:


                           (a) As soon as available and in any event within
          forty-five days after the end of each of the first three quarters of
          each fiscal year of the Borrower and its Subsidiaries, (i) an
          unaudited consolidated and consolidating balance sheet of the


                                      -5-

         Borrower and its Subsidiaries as of the end of such quarter and (ii)
         unaudited consolidated and consolidating statements of operations, cash
         flows and stockholders' equity of the Borrower and its Subsidiaries for
         the period commencing at the end of the previous fiscal year and ending
         with the end of such quarter, all in reasonable detail and duly
         certified by the chief financial officer or treasurer of the Borrower
         as having been prepared in accordance with generally accepted
         accounting principles consistently applied (subject to addition of
         notes and ordinary year-end audit adjustments), together with a
         certificate of the chief financial officer or treasurer of the Borrower
         stating that no Default or Event of Default has occurred and is
         continuing or, if a Default or an Event of Default has occurred and is
         continuing, a statement as to the nature thereof and the action that
         the Borrower proposes to take with respect thereto;

                           (b) As soon as available and in any event within
         ninety days after the end of each fiscal year of the Borrower, the
         audited consolidated balance sheet of the Borrower and its Subsidiaries
         as of the end of such fiscal year and the audited consolidated
         statements of operations, cash flows and stockholders' equity of the
         Borrower and its Subsidiaries for such fiscal year, in each case
         accompanied by the unqualified opinion with respect thereto of the
         Borrower's independent public accountants and a certification by such
         accountants stating that they have reviewed this Agreement and whether,
         in making their audit, they have become aware of any Default or Event
         of Default and if so, describing its nature, along with the related
         unaudited consolidating balance sheet of the Borrower and its
         Subsidiaries as of the end of such fiscal year and the unaudited
         consolidating statements of operations, cash flows and stockholders'
         equity of the Borrower and its Subsidiaries for such fiscal year;

                           (c) Concurrent with, and no later than the required
          date for delivery of the financial information outlined in Sections
          6.1(a) and (b), a certificate signed by the chief financial officer or
          treasurer of the Borrower substantially in the form of Exhibit D
          hereto (the "Compliance Certificate");

                           (d) Not later than forty-five days after the end of
          each fiscal year of the Borrower, the Borrower's representative
          forecast for the next fiscal year on a consolidated basis, including,
          at a minimum, projected statements of profit and loss and projected
          cash flow, prepared in accordance with generally accepted accounting
          principles consistently applied;

                           (e) Promptly upon receipt thereof, one copy of each
          other report submitted to the Borrower or any Subsidiary by
          independent accountants in connection with any annual, interim or
          special audit made by them of the books of the Borrower or any
          Material Subsidiary;

                           (f) Promptly after the commencement thereof, notice
          of all actions, suits and proceedings before any court, arbitration
          tribunal or governmental regulatory authority, commission, bureau,
          agency or public regulatory body that, if determined adversely to the
          Borrower or any Subsidiary of the Borrower, would be reasonably likely


                                      -6-

          to have a material adverse effect on the consolidated financial
          condition or results of operations of the Borrower and its
          Subsidiaries taken as a whole;

                           (g) As soon as possible, and in any event within five
          days after the Borrower shall know of the occurrence of any Default or
          Event of Default, the written statement of the chief financial officer
          or treasurer of the Borrower setting forth details of such Default or
          Event of Default and action that the Borrower proposes to take with
          respect thereto;

                           (h) As soon as possible, and in any event within five
          days after the occurrence thereof, written notice as to any other
          event of which the Borrower becomes aware that with the passage of
          time, the giving of notice or otherwise, is reasonably likely to
          result in a material adverse change in the consolidated financial
          condition or results of operations of the Borrower and its
          Subsidiaries taken as a whole;

                           (i) Promptly after Borrower becomes aware thereof,
          written notice of any noncompliance with ERISA that with the passage
          of time, the giving of notice or otherwise, is reasonably likely to
          result in a liability to the Borrower in excess of $1,000,000; and

                           (j) Such other information respecting the business or
          properties or the condition or operations, financial or otherwise, of
          the Borrower as the Lender may from time to time reasonably request.

         (D) Section 6.3(a) of the Loan Agreement is hereby deleted in its
entirety and replaced by the following:

                           (a) The Borrower will continue to engage in business
          of the same general nature as the business currently engaged in by the
          Borrower. The Borrower will at all times maintain, preserve and
          protect all material franchises and trade names and preserve all the
          Borrower's material tangible property used or useful in the conduct of
          its business and keep the same in good repair, working order and
          condition, ordinary wear and tear excepted, and from time to time make
          all needful and proper repairs, renewals, replacements, betterments,
          and improvements thereto so that the business carried on in connection
          therewith may be conducted properly and advantageously at all times;
          provided that nothing in this Section 6.3 shall prevent the Borrower
          from discontinuing the operation and maintenance of any of its
          properties or any of those of its Subsidiaries (including the
          voluntary liquidation and dissolution of a Subsidiary other than a
          Material Subsidiary) if such discontinuance is, in the judgment of the
          borrower, desirable in the conduct of its or their business and does
          not materially adversely affect the business of the Borrower and its
          Subsidiaries on a combined basis.

         (E) Article VI of the Loan Agreement is hereby further amended by the
addition of the following new Section 6.9:


                                      -7-

                  Guaranties. The Borrower shall cause any Subsidiary that
         becomes a Material Subsidiary promptly thereafter to execute and
         deliver a Guaranty to the Lender.

         (F) Article VII of the Loan Agreement is hereby deleted in its entirety
and replaced by the following:

                                  ARTICLE VII.


                       NEGATIVE COVENANTS OF THE BORROWER

                  The Borrower covenants and agrees that from the date of
          execution of this Agreement and until the payment in full of the
          principal of and interest upon the Notes and payment and performance
          of all other Obligations, unless the Lender shall otherwise consent in
          writing, the Borrower will not, and will not cause or permit any of
          its Subsidiaries to:

                  7.1 Sale of Assets; Mergers, Etc.

                           (a) Sale of Assets. Except for sales in the ordinary
         course of business, sell, transfer, or otherwise dispose of, to any
         Person any assets (including the securities of any Subsidiary) other
         than assets having an aggregate fair market value less than five
         percent (5%) of Borrower's Consolidated Tangible Net Worth.

                           (b) Mergers, Etc. Consolidate with or merge into any
         other Person or permit any other Person to consolidate with or merge
         into it, or acquire all or substantially all of the capital stock or
         assets of any Person, or sell, assign, lease or otherwise dispose of
         (whether in one transaction or in a series of transactions) all or
         substantially all of its assets to any Person, except that

                           (1) a Subsidiary may consolidate with or merge into,
                  or sell, assign, lease or otherwise dispose of any or all of
                  its assets to, the Borrower or another Subsidiary; and

                           (2) the Borrower or any of its Subsidiaries may
                  acquire all or substantially all of the capital stock or
                  assets of any Person or consolidate or merge with any Person
                  provided (i) such Person is engaged in a line of business
                  substantially similar to one or more of Borrower's existing
                  lines of business, (ii) the aggregate purchase price liability
                  incurred between the date hereof and the Revolver Termination
                  Date, including all contingent liabilities, when aggregated
                  with all such acquisitions and any Investments permitted under
                  Section 7.6(3) during such period shall not exceed
                  $20,000,000, and if 80% or more of the purchase price is paid
                  in


                                      -8-

                  capital stock of the Borrower, 20% of Consolidated Tangible
                  Net Worth as of the end of the most recent fiscal quarter,
                  (iii) based on a pro forma calculation of the ratios set forth
                  in Sections 7.9 - 7.11 as of the date such acquisition is
                  closed, assuming consolidation of the acquired business with
                  the Borrower for the four full fiscal quarters ended
                  immediately preceding such closing and pro forma debt and debt
                  service payments based on scheduled principal payments,
                  including acquisition borrowings, if any, and pro forma
                  interest on total debt at then prevailing borrowing rates,
                  Borrower is in compliance with the financial covenants set
                  forth in Sections 7.9 - 7.11, and (iv) all contingent
                  liability and contingent payment obligations incurred by
                  Borrower or any of its Subsidiaries in connection with such
                  transaction shall be reasonably acceptable to the Lender.

         7.2. Liens and Encumbrances.

                           (a) Create incur, assume or permit to exist any of
         its real or personal property, whether now owned or subsequently
         acquired, to be subject to any Lien other than Liens described below
         (which may herein be referred to as "Permitted Liens"):

                                    (1) Liens securing the payment of taxes,
                           assessments or governmental charges or levies or the
                           demands of suppliers, mechanics, carriers,
                           warehousers, landlords and other like Persons, which
                           payments are not yet due and payable or (as to taxes)
                           may be paid without interest or penalty; provided,
                           that, if such payments are due and payable, such
                           Liens shall be permitted hereunder only to the extent
                           that (A) all claims that the Liens secure are being
                           actively contested in good faith and by appropriate
                           proceedings, (B) adequate book reserves have been
                           established with respect thereto to the extent
                           required by generally accepted accounting principles,
                           and (C) such Liens do not in the aggregate materially
                           interfere with the owning company's use of property
                           necessary or material to the conduct of the business
                           of the Borrower and its Subsidiaries taken as a
                           whole;

                                    (2) Liens incurred or deposits made in the
                           ordinary course of business (A) in connection with
                           worker's compensation, unemployment insurance, social
                           security and other like laws, or (B) to secure the
                           performance of letters of credit, bids, tenders,
                           sales contracts, leases, statutory obligations,
                           surety, appeal and performance bonds and other
                           similar obligations, in each


                                      -9-

                           case not incurred in connection with the borrowing of
                           money, the obtaining of advances or the payment of
                           the deferred purchase price of property;

                                    (3) Liens not otherwise described in Section
                           7.2(a)(1) or (2) that are incurred in the ordinary
                           course of business and are incidental to the conduct
                           of its business or ownership of its property, were
                           not incurred in connection with the borrowing of
                           money, the obtaining of advances or the payment of
                           the deferred purchase price of property and do not in
                           the aggregate materially detract from the value of,
                           or materially interfere with the owning company's use
                           of, property necessary or material to the conduct of
                           the business of the Borrower and its Subsidiaries
                           taken as a whole;

                                    (4) Liens in favor of the Lender;

                                    (5) Judgment liens or attachments that shall
                           not have been in existence for a period longer than
                           30 days after the creation thereof, or if a stay of
                           execution shall have been obtained, for a period
                           longer than 30 days after the expiration of such stay
                           or if such an attachment is being actively contested
                           in good faith and by appropriate proceedings, for a
                           period longer than 30 days after the creation
                           thereof;

                                    (6) Liens existing as of the Closing Date
                           and disclosed on the Disclosure Schedule hereto;

                                    (7) Liens provided for in equipment or
                           Financing Leases (including financing statements and
                           undertakings to file financing statements) provided
                           that they are limited to the equipment subject to
                           such leases and the proceeds thereof;

                                    (8) Leases or subleases with third parties
                           or licenses and sublicenses granted to third parties
                           not interfering in any material respect with the
                           business of the Borrower or any Subsidiary of the
                           Borrower;

                                    (9) Any Lien on any asset of any corporation
                           existing at the time such corporation is merged into
                           or consolidated with (or acquired in accordance with
                           Section 7.1(b) by) the Borrower or a Subsidiary of
                           the Borrower and not created in contemplation of such
                           event;


                                      -10-

                                    (10) Any Lien existing on any asset prior to
                           the acquisition thereof by the Borrower or any
                           Subsidiary of the Borrower and not created in
                           contemplation of such event;

                                    (11) Liens in respect of any purchase money
                           obligations for tangible property used in its
                           business, which obligations shall not at any time
                           exceed 5% of Consolidated Tangible Net Worth,
                           provided that any such encumbrances shall not extend
                           to property and assets of the Borrower or any
                           Subsidiary not financed by such a purchase money
                           obligation;

                                    (12) Easements, rights of way, restrictions
                           and other similar charges or Liens relating to real
                           property and not interfering in a material way with
                           the ordinary conduct of its business; and

                                    (13) Liens on its property or assets created
                           in connection with the refinancing of Indebtedness
                           secured by Permitted Liens on such property, provided
                           that the amount of Indebtedness secured by any such
                           Lien shall not be increased as a result of such
                           refinancing and no such Lien shall extend to property
                           and assets of the Borrower or any Subsidiary not
                           encumbered prior to any such refinancing.

                           (b) In case any property is subjected to a Lien in
                  violation of Section 7.2(a), the Borrower will make or cause
                  to be made provision whereby the Note will be secured equally
                  and ratably with all other obligations secured by such
                  property, and in any case the Note shall have the benefit, to
                  the full extent that the holder may be entitled thereto under
                  applicable law, of an equitable Lien equally and ratably
                  securing the Note. Such violation of Section 7.2(a) shall
                  constitute an Event of Default hereunder, whether or not any
                  such provision is made pursuant to this Section 7.2(b).

                           (c) None of the equity interests of the Borrower or
                  any Subsidiary in any Subsidiary is subject to any Lien
                  (including any Permitted Lien), and neither the Borrower nor
                  any Subsidiary will agree with any third party not to cause or
                  permit any of its real or personal property, whether now owned
                  or subsequently acquired, to be subject to Liens (with or
                  without exceptions).

                           (d) Cause or permit or (ii) agree or consent to cause
                  or permit in the future (upon the happening of a contingency
                  or otherwise), any of its equity interests in any Subsidiary
                  to be subject to any Lien (including any Permitted Lien).


                                      -11-

                  7.3 Sales and Leasebacks. Sell or transfer any of their
         property and become, directly or indirectly, liable as the lessee under
         a lease of such property (other than such transactions between the
         Subsidiaries and transfers of capital equipment that will be leased
         pursuant to Financing Leases).

                  7.4 Indebtedness. Create, incur or assume any Indebtedness
         other than:

                           (1) Indebtedness to the Lender pursuant to this
                  Agreement and Indebtedness pursuant to the Credit Agreement;

                           (2) Financing Lease Obligations, not to exceed
                  $10,000,000 in the aggregate at any one time outstanding;

                           (3) Endorsements for collection, deposit or
                  negotiation and warranties of products or services, in each
                  case incurred in the ordinary course of business;

                           (4) Subordinated Debt:

                           (5) Indebtedness of the Borrower owing to
                  Subsidiaries not otherwise permitted by this Section 7.4 in an
                  aggregate principal amount at any time outstanding not to
                  exceed $5,000,000;

                           (6) Indebtedness of Subsidiaries owing to the
                  Borrower not otherwise permitted by this Section 7.4 in an
                  aggregate principal amount at any time outstanding not to
                  exceed $5,000,000;

                           (7) Indebtedness of any wholly-owned Subsidiary owing
                  to any other wholly-owned Subsidiary;

                           (8) Guarantees by Material Subsidiaries of the
                  Obligations;

                           (9) Indebtedness with respect to Investments
                  permitted by Section 7.6(3) so long as such entities remain
                  Subsidiaries or Affiliates of the Borrower; and

                           (10) Indebtedness not included above and listed on
                  the Disclosure Schedule.

                   7.5 Dividends and Distributions. Declare or pay, directly or
          indirectly, any dividend (other than a dividend payable solely in the
          Common Stock of the Borrower) or make any other distribution (by
          reduction of capital or otherwise), whether in cash, property,
          securities or a combination thereof, with respect to any shares of its
          capital stock or, directly or indirectly, except to the extent
          permitted by Section 6.2 hereof, redeem, purchase, retire or otherwise
          acquire for value any shares of any class of its capital stock or set
          aside any amount for any such


                                      -12-

         purpose; provided, however, that any Subsidiary of the Borrower may
         declare and pay dividends or make other distributions to the Borrower.

                  7.6 Investments. Except as permitted by Section 7.1, make or
         maintain any investments, made in cash or by delivery of property or
         assets, (a) in any Person, whether by acquisition of capital stock,
         Indebtedness, or other obligations or securities, or by loan or capital
         contribution, or otherwise, or (b) in any property, whether real or
         personal, (items (a) and (b) being herein called "Investments") except
         the following (but only with funds other than proceeds of Advances):

                           (1) Investments in direct obligations of, or
                  guaranteed by, the United States government, its agencies or
                  any public instrumentality thereof and backed by the full
                  faith and credit of the United States government with
                  maturities not to exceed (or an unconditional right to compel
                  purchase within) three years from the date of acquisition;

                           (2) Repurchase agreements collateralized by
                  securities of the U.S. Government and U.S. Government-
                  sponsored securities;

                           (3) Investments in or to any Subsidiary or other
                  Affiliate, provided Borrower remains in compliance with
                  Section 7.1(b);

                           (4) Investments and obligations issued by the United
                  States government, any agency thereof, any state of the United
                  States or any political subdivision of any such state or any
                  public instrumentality thereof with maturities not to exceed
                  (or an unconditional right to compel purchase within) three
                  years from the date of acquisition that are rated AA- or
                  higher by at least one nationally recognized rating agency;

                           (5) Investments and obligations issued by any company
                  (other than a bank) with maturities not to exceed three years
                  from the date of acquisition with a long-term debt rating of A
                  or higher or a short-term debt rating of A1 or P1 by at least
                  one nationally recognized rating agency;

                           (6) Investments in demand and time deposits with,
                  Eurodollar deposits with, certificates of deposit issued by,
                  or obligations or securities fully backed by letters of credit
                  issued by (x) any bank organized under the laws of the United
                  States, any state thereof, the District of Columbia or Canada
                  having combined capital and surplus aggregating at least
                  $500,000,000, or (y) any


                                      -13-

                  other bank organized under the laws of a state that is a
                  member of the European Economic Community (or any political
                  subdivision thereof), Japan, the Cayman Islands, or British
                  West Indies having as of any date of determination combined
                  capital and surplus of not less than $500,000,000 or the
                  equivalent thereof (determined in accordance with generally
                  accepted accounting principles);

                           (7) Shares of money market mutual funds registered
                  under the Investment Company Act of 1940, as amended;

                           (8) Foreign currency swaps and hedging arrangements
                  entered into in the ordinary course of business to protect
                  against currency losses, and interest rate swaps and caps
                  entered into in the ordinary course of business to protect
                  against interest rate exposure on Indebtedness bearing
                  interest at a variable rate;

                           (9) Investments in mutual funds (other than money
                  market mutual funds and short term bond funds with individual
                  maturities under three years and aggregate ratings of A- or A3
                  or higher by at least one nationally recognized rating agency)
                  that in the aggregate shall not exceed $5,000,000;

                           (10) Investments in the form of advances to employees
                  in the ordinary course of business for moving, entertainment,
                  travel and other similar expenses, but not more than
                  $1,000,000 in the aggregate outstanding at any time; and

                           (11) Other Investments existing on the Closing Date
                  and listed on the Disclosure Schedule.

                  7.7 Transactions with Affiliates. Enter into any transaction
         (including the purchase, sale or exchange of property or the rendering
         of any service) with any Affiliate except upon fair and reasonable
         terms that are at least as favorable to the Borrower or the Subsidiary
         as would be obtained in a comparable arm's-length transaction with a
         non-Affiliate.

                  7.8 ERISA Compliance. Permit any employee pension benefit plan
         (as such term is defined in Section 3 of ERISA) maintained by the
         Borrower or any of its Subsidiaries or in which employees of the
         Borrower or any of its Subsidiaries is entitled to participate to:

                           (a)      engage in any "prohibited transaction" as
                                    such term is defined in Section 4975 of the
                                    Internal Revenue Code of 1986, as amended,
                                    or described in Section 406 of ERISA;


                                      -14-

                           (b)      incur any "accumulated funding deficiency"
                                    as such term is defined in Section 302 of
                                    ERISA, whether or not waived; or

                           (c)      terminate under circumstances that could
                                    result in the imposition of a Lien on the
                                    property of the Borrower or any Subsidiary
                                    of the Borrower pursuant to Section 4068 of
                                    ERISA.

                  7.9 Tangible Net Worth Test. Permit the Consolidated Tangible
          Net Worth as of the end of each fiscal quarter of the Borrower to be
          less than the sum of (i) $292,000,000, plus (ii) 80% of Consolidated
          Net Income (excluding losses), plus (iii) the net proceeds of any
          equity securities sold by the Borrower after June 30, 2001, for each
          consecutive fiscal quarter of the Borrower beginning with the quarter
          ending September 30, 2001, on a cumulative basis.

                  7.10 Total Liabilities-to-Tangible Net Worth Ratio. Permit the
          ratio ("Total Liabilities-to-Tangible Net Worth Ratio") of the
          Consolidated Total Liabilities as of the end of each fiscal quarter of
          the Borrower beginning with the fiscal quarter ending September 30,
          2001 to its Consolidated Tangible Net Worth as of the end of each
          fiscal quarter of the Borrower beginning with the fiscal quarter
          ending September 30, 2001 to exceed 1 to 1.

                  7.11 Quick Ratio. Permit the ratio (the "Quick Ratio") of (i)
         Consolidated Quick Assets to (ii) Consolidated Current Liabilities to
         be less than 2.25 to 1.00.


                  7.12 Capital Expenditures. Make capital expenditures that in
          the aggregate and on a consolidated basis exceed during each fiscal
          quarter of the Borrower the sum of $7,000,000 plus the amount by which
          such expenditures during the immediately preceding quarter, beginning
          with the quarter ended September 30, 2001, were less than $7,000,000.

                  7.13 Contracts Prohibiting Compliance with Agreement. Enter
         into any contract or other agreement that would prohibit or in any way
         restrict the ability of the Borrower to comply with any provision of
         this Agreement.

          (G) Article VIII of the Loan Agreement is hereby amended by the
replacement of existing subsections 8.1(c), (d) (e), (f) and (m) with the
following:

                                    (c) A final judgment or settlement for in
                  excess of $3,000,000 shall be rendered against or agreed to by
                  the


                                      -15-

                  Borrower or any of its Subsidiaries for the payment of money
                  that, after deducting the amount of any insurance proceeds
                  paid or payable to or on behalf of the Borrower or its
                  Subsidiary in connection with such judgment or settlement, as
                  the case may be, is in excess of $3,000,000, and such judgment
                  shall remain undischarged for a period of thirty (30) days,
                  during which period execution shall not effectively be stayed,
                  or such settlement shall remain unpaid for a period of thirty
                  days after the agreed payment date unless such delay has been
                  agreed to by the other party. If a dispute exists with respect
                  to the liability of any insurance underwriter under any
                  insurance policy of the Borrower or its Subsidiary, no
                  deduction under this subsection shall be made for the
                  insurance proceeds that are the subject of such dispute;

                                   (d) The Borrower or any Subsidiary (except to
                  the extent explicitly permitted by this Agreement), shall (1)
                  voluntarily terminate operations or apply for or consent to
                  the appointment of, or the taking of possession by, a
                  receiver, custodian, trustee or liquidator of such Person or
                  of all or a substantial part of the assets of such Person, (2)
                  admit in writing its inability, or be generally unable, to pay
                  its debts as the debts become due, (3) make a general
                  assignment for the benefit of its creditors, (4) commence a
                  voluntary case under the Federal Bankruptcy Code (as now or
                  hereafter in effect), (5) file a petition seeking to take
                  advantage of any other law relating to bankruptcy, insolvency,
                  reorganization, winding-up, or composition or adjustment of
                  debts, (6) fail to controvert in a timely and appropriate
                  manner, or acquiesce in writing to, any petition filed against
                  it in an involuntary case under the Federal Bankruptcy Code or
                  applicable state bankruptcy laws or (7) take any corporate
                  action for the purpose of effecting any of the foregoing;

                                   (e) Without its application, approval or
                  consent, a proceeding shall be commenced, in any court of
                  competent jurisdiction, seeking in respect of the Borrower or
                  any domestic Subsidiary: the liquidation, reorganization,
                  dissolution, winding-up, or composition or readjustment of
                  debt, the appointment of a trustee, receiver, liquidator or
                  the like of such Person or of all or any substantial part of
                  the assets of such Person, or other like relief in respect of
                  such Person under any law relating to bankruptcy, insolvency,
                  reorganization, winding-up, or composition or adjustment of
                  debts; and, if the proceeding is being contested in good faith
                  by such Person, the same shall continue undismissed, or
                  unstayed and in effect for any period of 45 consecutive days,
                  or an order for relief against such Person shall be


                                      -16-

                  entered in any case under the Bankruptcy Code or applicable
                  state bankruptcy laws;

                                    (f) Any foreclosure or other proceedings
                  shall be commenced to enforce, execute or realize upon any
                  lien, encumbrance, attachment, trustee process, mortgage or
                  security interest for payment of an amount in excess of
                  $500,000 against the Borrower or any Subsidiary;

                                    (m) There shall occur a Change in Control;

                  Section 2. Representations and Warranties. The Borrower hereby
represents and warrants as follows:

                  (a) The execution and delivery of this Amendment and the
performance of this Amendment, the Loan Agreement as amended hereby and each of
the other Loan Documents, and the transactions contemplated hereby and thereby,
have been authorized by all necessary corporate actions of the Borrower. This
Amendment, the Loan Agreement as amended hereby and each of the other Loan
Documents constitute the legal, valid and binding obligations of the Borrower,
enforceable against the Borrower in accordance with their respective terms.

                  (b) The Borrower has all requisite corporate power and
authority to execute, deliver and perform its obligations under this Amendment,
the Loan Agreement as amended hereby and each of the other Loan Documents.
Neither the authorization, execution, delivery or performance by the Borrower of
this Amendment nor the performance of the Loan Agreement as amended hereby or
any other Loan Document nor the performance of the transactions contemplated
hereby or thereby violates or will violate any provision of the corporate
charter or by-laws of the Borrower, or does or will, with the passage of time or
the giving of notice or both, result in a breach of or a default under, or
require any consent under or result in the creation of any lien, charge or
encumbrance upon any property or assets of the Borrower pursuant to, any
material instrument, agreement or other document to which the Borrower is a
party or by which the Borrower or any of its properties may be bound or
affected.

                  (c) The execution and delivery by the Borrower of this
Amendment and the performance by the Borrower of the Loan Agreement as amended
hereby and the Loan Documents do not and will not violate any provision of law
or regulation applicable to the Borrower, or any writ, order or decree of any
court or governmental or regulatory authority or agency applicable to the
Borrower.

                  (d) The representations and warranties contained in Article IV
of the Loan Agreement are true and correct, and the Borrower and its
Subsidiaries are in compliance with all covenants set forth in Article VII of
the Loan Agreement, provided that for this purpose that all references to the
"Disclosure Schedule" in such Articles IV and VII shall be deemed to mean the
Disclosure Schedule attached hereto, which is true and complete.


                                      -17-

         Section 3. Loan Documents. This Amendment shall be a Loan Document for
all purposes.

         Section 4. Conditions to Effectiveness. The effectiveness of this
Amendment is conditioned on the following:

                  (a) The Borrower and the Lender shall each have executed and
delivered a counterpart of this Amendment;

                  (b) The representations and warranties contained in Article IV
of the Loan Agreement shall be true and correct in all material respects as of
the date hereof as though made on and as of the date hereof;

                  (c) No Default or Event of Default under the Loan Agreement
shall have occurred and be continuing;

                  (d) The conditions set forth in Sections 5.2-5.5 of the Loan
Agreement shall have been met as of the date hereof, provided that for purposes
thereof and Section 4.5 of the Loan Agreement, the "Balance Sheet Date" shall
mean June 30, 2001 and the financial statements referred to therein shall mean
the unaudited statements for the period ended June 30, 2001, that have been
furnished to the Lender.

                  (e) The Lender shall have received a certificate of the clerk
of the Borrower as to the votes of Borrower's directors authorizing the
execution and delivery of this Amendment and the incumbency of the officers
authorized to execute this Amendment on behalf of the Borrower and a certificate
of the secretary of each of the Guarantors as to the votes of such Guarantor's
directors authorizing the execution and delivery of the Guaranty and the
incumbency of the officers authorized to execute the Guaranty on behalf of such
Guarantor.

         Section 5. Miscellaneous.

                  (a) On and after the date hereof, each reference in the Loan
Agreement to "this Agreement" or words of like import shall mean and be deemed
to be a reference to the Loan Agreement as amended hereby.

                  (b) Except as amended and modified hereby, the Loan Agreement
is in all respects ratified and confirmed as of the date hereof, and the terms,
covenants and agreements therein shall remain in full force and effect.

                  (c) This Amendment and the modifications to the Loan Agreement
set forth herein shall be deemed to be a document executed under seal and shall
be governed by and construed in accordance with the laws of The Commonwealth of
Massachusetts.

                  (d) This Amendment may be executed in counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same document.

                  [Remainder of page intentionally left blank.]


                                      -18-

                  IN WITNESS WHEREOF, the parties have caused this Amendment to
be duly executed as of the date and the year first above written.

                                          MKS INSTRUMENTS, INC.


                                          By: /s/ William P Donlan
                                              ---------------------------
                                              Title: Treasurer


                                          FLEET NATIONAL BANK


                                          By: /s/ Daniel G. Head Jr.
                                              ---------------------------
                                              Title: Director



                                      -19-