Document:

<PAGE>

                             CONFIDENTIAL TREATMENT

                                                                    Exhibit 10.1

                           MEMORANDUM OF UNDERSTANDING

between

DSM Fine Chemicals Netherlands B.V.
Noorderpoort 9, 5900 AB Venlo, The Netherlands
(hereinafter referred to as "DSM")

and

Cubist Pharmaceuticals, Inc..
24 Emily Street, Cambridge, MA 02139, USA
(hereinafter referred to as "CUBIST")

CUBIST has a project to introduce a new pharmaceutical, which will consume
DAPTOMYCIN, a lipopeptide antibiotic bulk drug substance.

CUBIST is interested in engaging DSM as a supplier of Daptomycin and DSM is
interested in manufacturing and supplying Daptomycin to CUBIST in accordance
with the principles set forth in this MOU.

This memorandum represents the joint understanding of both companies regarding
the future supply of DAPTOMYCIN.

DSM is the signatory to this Memorandum on behalf of all DSM affiliate companies
which are involved in the development and production of DAPTOMYCIN.

1.  INVESTMENTS

DSM agrees to carry out the investments described in Annex 1 to this MOU at its
Capua site which are required to construct a bulk drug facility for the
production of DAPTOMYCIN in accordance with cGMP standards. DSM further agrees
to test and validate this bulk drug facility in accordance with cGMP standards.
<PAGE>

Construction, testing and validation of such facility shall be finalized within
12 months from the execution of this MOU.

2.  COST REIMBURSEMENT

CUBIST agrees to reimburse DSM [ ]* which will be incurred by DSM in connection
with the carrying out of the above described investments, testing and validation
up to an aggregate maximum amount of [ ]*. A preliminary cost estimation as well
as the payment schedule are attached to this MOU as Annex 2. The parties agree
that the above limit of [ ]* is based on the investments described in Annex 1.
In the event CUBIST should demand modifications of said investments and/or
additional investments which lead to increased costs to DSM, CUBIST will fully
reimburse DSM also for such part of the costs which exceed the above limit of
[ ]*.

3.  CONTRACT

A detailed contract regarding the carrying out of the investments (including
cost reimbursement) and regarding the long-term supply of DAPTOMYCIN
(hereinafter called "definitive Supply Agreement") is targeted to be signed by
both companies before [ ]*. The definitive Manufacturing and Supply Agreement
will cover the years up to and including [ ]*, and will include the terms stated
in this MOU plus standard representation and warranties; standard non-disclosure
and publicity clauses; standard covenants and clauses regarding: enabling
licenses; ownership and retention of intellectual property rights; information
exchange; order, delivery and acceptance procedures; quality control; product
recalls; traceability program; maintenance of cost and production records; risk
allocation (indemnity and insurance); failure to perform, termination;
assignment and independent status. After [ ]*, the definitive Manufacturing and
Supply Agreement will have evergreen conditions for periods of one year with one
year's notice for cancellation.

4.  MINIMUM VOLUMES

From [ ]* until [ ]* CUBIST will purchase from DSM an aggregate minimum quantity
of [ ]* kgs of DAPTOMYCIN. Notwithstanding the foregoing sentence the minimum
volumes of DAPTOMYCIN to be purchased by CUBIST from DSM per single calendar
year are

[    ]*

*  Confidential treatment requested: Material has been omitted and filed with
   the Commission.

<PAGE>

Subject to sufficient lead time (Art. 7) DSM agrees to cover an additional
demand of CUBIST for DAPTOMYCIN up to [ ]* kgs per year.

6.  PRICING / DELIVERY TERMS.

During the initial term of the definitive Supply Agreement the price for
DAPTOMYCIN shall be [ ]*-- per kg.

If CUBIST's purchases of DAPTOMYCIN from DSM in [ ]* have cumulatively surpassed
a volume of [ ]* kgs and CUBIST's binding orders for DAPTOMYCIN for [ ]* and
[ ]* exceed an aggregate volume of [ ]* kgs, the parties will negotiate in good
faith a reasonable reduction of the per kg price valid in [ ]*.

Delivery dates will be discussed [ ]* in advance.

7.  ROLLING FORECAST

[ ]* in advance of every year, on a quarterly basis, volumes of DAPTOMYCIN will
be fixed for the year to come [ ]*. In addition, CUBIST will provide DSM with a
quarterly rolling forecast of DAPTOMYCIN volumes for the subsequent four
quarters.

8.  IMPROVEMENTS: INTELLECTUAL PROPERTY RIGHTS

DSM will implement the CUBIST Process (which will be clearly defined in an Annex
of the definitive Manufacturing and Supply Agreement) and will not research or
significantly alter this process. In the event the parties agree to undertake
any research, development or enhancement of the process they shall enter into a
separate agreement concerning such activity. DAPTOMYCIN-specific process
improvements and technology will remain the property of CUBIST, while general
knowhow relating to fermentation and manufacturing knowhow will remain the
property of DSM.

CUBIST shall be responsible and indemnify DSM against all loss, liability,
damage and expense incurred by DSM and DSM affiliate companies which are
involved in the development and production of DAPTOMYCIN arising out of any
infringement of intellectual property rights of third parties in connection with
the manufacture of DAPTOMYCIN in accordance with the CUBIST Process.

*  Confidential treatment requested: Material has been omitted and filed with
   the Commission.

<PAGE>

9.  CONFIDENTIALITY

Terms and conditions similar to those set forth in the Secrecy Agreement between
CUBIST and DSM dated May 11, 1999 shall be agreed in the definitive
Manufacturing and Supply Agreement mutatis mutandis.

10.  AFFILIATES

The parties agree that they may have their rights and obligations performed by
their respective affiliates, however, each party shall not be relieved from its
obligations hereunder and shall remain liable for their performance hereunder.

11.  GOVERNING LAW. ARBITRATION

This Memorandum of Understanding is (and the subsequent definitive Manufacturing
and Supply Agreement will be) subject to the laws of the United Kingdom
excluding its conflict of law rules. Disputes that cannot be solved amicably
shall be finally settled by arbitration according to the Arbitration Rules of
the London Court of Intentional Arbitration (LCIA) by one or more arbitrators
appointed in accordance with such Rules. Venue of arbitration shall be London,
U.K. and the language of arbitration shall be English.

12.  EFFECTIVE DATE

This Memorandum of Understanding shall become effective upon execution by both
parties and approval of the investment by the Board of DSM and shall remain
valid until the signature of the contemplated definitive Supply Agreement.

DEVELOPMENT PROPOSAL

The parties have agreed upon a program for the technology transfer, design,
validation and production of [ ]* NDA qualification batches in a total value of
[ ]*. This program is subject to a separate agreement between the parties and is
not amended or superseded by this MOU.

*  Confidential treatment requested: Material has been omitted and filed with
   the Commission.

<PAGE>

In connection with this program the parties have agreed upon the following
milestone payments:

<TABLE>
<CAPTION>
PAYMENT                   MILESTONE                                                           TIMING

<S>  <C>                                                                                      <C>
[   ]*

-    if the manufacture of the [ ]* consistency batches and the preparation of
     NDA documents (milestone 5) are completed after [ ]* but before [ ]*,
     CUBIST shall pay to DSM an amount of [ ]*,--.

-    If the manufacture of the [ ]* consistency batches and the preparation of
     NDA documents (milestone 5) are completed before [ ]*, CUBIST shall pay to
     DSM an additional amount of [ ]*,--.

-    If the manufacture of the [ ]* consistency batches and the preparation of
     NDA documents (milestone 5) are completed after [ ]*, DSM shall pay to
     CUBIST an amount of [ ]*.
</TABLE>

Dutch State Mines Fine Chemicals              Cubist Pharmaceuticals, Inc.
Netherlands B.V.

/s/ Henk Nuwman                               /s/ Scott M. Rocklage
-----------------------------------------     ---------------------------------
H. Nuwman                                     Scott M. Rocklage
Business Unit Director                        President & CEO

Date:  1/26/00                                Date:  1/4/00

*  Confidential treatment requested: Material has been omitted and filed with
   the Commission.<PAGE>

                            SECOND AMENDED AND RESTATED

                              JOINT VENTURE AGREEMENT
                              -----------------------

     THIS SECOND AMENDED AND RESTATED JOINT VENTURE AGREEMENT (the "Agreement")
is made and entered into as of the 1st day of January 2000, by and between Blue
Cross & Blue Shield United of Wisconsin, a Wisconsin Chapter 613 insurance
corporation ("Blue Cross"), United Wisconsin Services, Inc., a Wisconsin Chapter
180 business corporation ("UWS"), Valley Health Plan, Inc., a Wisconsin Chapter
611 insurance corporation ("VHP"), and Midelfort Clinic, Ltd., Mayo Health
System, a Wisconsin Chapter 181 business corporation (the "Clinic").

                                      PREAMBLE
                                      --------

     WHEREAS, Blue Cross and the Clinic entered into a Joint Venture Agreement
dated January 1, 1992 for the purpose of enhancing their respective businesses
by offering managed care products which utilize a provider network;

     WHEREAS, the January 1, 1992 Joint Venture Agreement was subsequently
amended and restated effective January 1, 1997;

     WHEREAS, the parties wish to amend the January 1, 1997 Agreement by
entering into a new agreement to become effective January 1, 2000 (the "Second
Amended and Restated Joint Venture Agreement") and to amend the prior joint
venture agreements as set forth herein;

     WHEREAS, the Clinic has sold Midelfort Health Plan, Inc.

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("MHP", n/k/a VHP) to UWS while retaining an option to repurchase, under a
Purchase and Sale Agreement dated as of January 1, 1992 ("Purchase and Sale
Agreement"), amended effective January 1, 1997 and subsequently amended
effective January 1, 2000;

     WHEREAS, the parties wish to coordinate the design and marketing of various
managed care insurance products which utilize a provider network, including,
without limitation, Point of Service ("POS") and Health Maintenance Organization
("HMO") products and programs;

     WHEREAS, the Clinic shall participate in the offering of these products by
serving as the primary provider and by assisting in the design and marketing of
the products;

     WHEREAS, the underwriters shall be liable for losses incurred by the
products, but shall share with the Clinic the collective profits of the products
as specified in Article 5, herein; and

     WHEREAS, Midelfort Clinic, Ltd. (which has been acquired by Mayo Foundation
for Medical Education and Research) and the other parties to this Agreement have
consented to the assignment by Midelfort Clinic, Ltd. to Midelfort Clinic, Ltd.,
Mayo Health System, all of its rights, title and interest in, to and under the
prior joint venture agreements and this Second Amended and Restated Joint
Venture Agreement.

     NOW THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows:

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                               1.  SCOPE OF AGREEMENT
                               ----------------------

     1.1  Blue Cross shall be defined herein to include all its respective
          subsidiaries and affiliates except where UWS is referred to
          specifically.  The Clinic shall be defined herein to include all its
          respective subsidiaries and affiliates in which the Clinic has an
          ownership interest (but not its sole member).

     1.2  The parties to this Agreement have entered into a series of related
          contracts with one another in order to produce, market, and administer
          managed care insurance products which utilize a provider network.  The
          relationships between and among the parties are that of independent
          contractors working together in a cooperative arrangement.  It is not
          the intent of the parties to create, nor should this Agreement be
          construed to create, a partnership or an employment relationship
          between or among the parties.

     1.3  This Agreement shall not create any agency relationship between or
          among the parties other than those specifically enumerated in provider
          agreements and administrative services agreements entered into between
          Blue Cross and/or VHP, as the underwriters, and the Clinic.  This
          Agreement creates no fiduciary relationship between or among any of
          the parties.

                                          -3-

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                                    2.  PRODUCTS
                                    ------------

     2.1  The parties will design and market various insured managed care
          products which utilize a provider network, including POS and HMO
          products.  Hereafter, these products may be collectively referred to
          as "Insured Products."

     2.2  Blue Cross shall be the underwriter of the indemnity segment of POS
          plans and VHP shall be the underwriter of the HMO plans (Blue Cross
          and VHP are in this role collectively referred to as the
          "Underwriters").

     2.3  The Clinic shall be the primary provider for all products contemplated
          by this Agreement.  The Clinic shall enter into provider agreements
          with the Underwriters to carry out the purposes of this Agreement.

     2.4  It is the intent of Blue Cross and the Clinic to cooperate in the
          design and development of a Medicare Risk product and a managed care
          Workers' Compensation product at such time that the parties mutually
          agree that economic and market conditions are favorable.

                                3.  GOVERNING BOARD
                                -------------------

     3.1  The cooperative arrangement contemplated by this Agreement shall be
          directed through a Governing Board. Blue Cross and the Clinic shall
          each select four

                                          -4-

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          members of the Governing Board.  The Governing Board
          may select a smaller executive committee to manage the joint venture
          on a day-to-day basis subject to the control of the Governing Board.

     3.2  With respect to the Insured Products, all major policies and decisions
          regarding the Underwriter's business plan, marketing, benefit design,
          public relations, provider contracting (including capitation and fee
          schedule contracts), administrative services agreements, and medical
          underwriting guidelines shall be subject to approval by the Governing
          Board.  Notwithstanding the foregoing, the direct Underwriter shall
          have ultimate authority on Insured Products in setting rates, medical
          underwriting functions and reinsurance.  VHP shall arrange for
          reinsurance for plans it underwrites through a competitive bid
          process. Selection of the reinsurer shall be based on price and cost
          control services offered by the reinsurer. Notwithstanding the
          foregoing, VHP's selection of a reinsurer is subject to the prior
          approval of the Governing Board.

     3.3  In the event the positions of Director of VHP and/or the primary
          Medical Director for VHP become vacant, the recommended candidate for
          either position will require the approval of the Governing Board.

     3.4  The four members of the Governing Board selected by

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          Blue Cross shall be responsible for selecting, negotiating and
          terminating contracts with other independent providers, who are not
          otherwise affiliates of the Clinic or members of the Mayo Health
          System, on behalf of the Underwriters subject to the following
          conditions and restrictions:

          (a)  The four members of the Governing Board selected by the Clinic
               shall be solicited to offer comments relating to the selection of
               and contracting with independent providers or their termination.
               Upon receipt of comments offered by the Clinic's Governing Board
               members, a majority vote solely of the four Blue Cross members of
               the Governing Board shall determine which such providers are
               selected, the contract terms offered and afforded them and if and
               when their contracts are terminated.

          (b)  Notwithstanding the foregoing, if any such independent providers
               are afforded contract terms which are, in whole or in particular
               part, more favorable to such providers than those afforded the
               Clinic under its provider agreements with the Underwriters, such
               more favorable terms shall automatically and without further
               action of the parties be incorporated in such agreements with the
               Clinic and shall remain in place so long as such terms are
               afforded one or more independent

                                          -6-

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               providers.

          (c)  In selecting independent providers, the Blue Cross members of the
               Governing Board shall duly consider:  the medical credentials of
               such providers; whether the provider's credentials meet standards
               set by the National Committee for Quality Assurance or other
               accrediting agency acceptable to the Governing Board; whether
               there is a need for their participation in order to provide an
               adequate and appropriate level of medical services to insureds;
               whether the addition of such providers and the contract terms to
               be afforded them are consistent with and will promote the
               provision of managed medical care on a cost-efficient basis; and
               such other factors as are reasonably deemed relevant by the Blue
               Cross members of the Governing Board.

          (d)  Each application of an independent provider shall be duly
               considered by the Blue Cross members of the Governing Board on a
               timely basis and such members' decision on each such application
               shall be timely communicated to the applicant.

                                          -7-

<PAGE>

                       4.  SERVICE AGREEMENTS AND PAYMENT TERMS
                       ----------------------------------------

     4.1  The Governing Board and executive committee members shall be
          compensated for their services to the joint venture through
          administrative services agreements.  It is anticipated that the
          Clinic, through administrative services agreements, will provide
          quality assurance and medical management services to the
          Underwriters. All administrative services agreements must be approved
          by the Governing Board.

     4.2  The terms of the administrative services agreements shall provide that
          the Clinic and Blue Cross shall be compensated for their services on
          an Actual Cost basis such that all administrative profit remains with
          the Underwriters to be shared through the profit sharing arrangements
          set forth in Article 5 below.  "Actual Cost" as used herein, shall be
          defined as direct costs and indirect cost allocation as provided for
          in the administrative services agreements.

     4.3  VHP will enter into provider agreements with the Clinic to be the
          primary provider within the network for the HMO and POS products and
          the Medicare Supplement product.  The terms of the provider agreements
          shall provide:

          (a)  POS PRODUCT:  Effective January 1, 2000, VHP will reimburse the
               Clinic at the Clinic's charges less a discount of thirteen
               percent (13%) for VHP's POS

                                          -8-

<PAGE>

               product.

          (b)  MEDICARE SUPPLEMENT PRODUCT:  Effective January 1, 2000, the
               capitation rate for VHP's Medicare Supplement product will be
               increased by five percent (5%) over the rate in effect for
               calendar year 1999.  In calendar years 2001 and 2002,
               respectively, the capitation rate will be increased by five
               percent (5%) over the rate in effect for calendar years 2000 and
               2001, respectively.

          (c)  COMMERCIAL HMO PRODUCTS:  Effective January 1, 2000, the
               capitation rate for VHP's commercial HMO products will be
               increased by twelve percent (12%) over the rate in effect for
               calendar year 1999 as set forth in Attachment A.  Effective
               January 1, 2001, the capitation rate shall be the capitation rate
               for calendar year 2000 increased by the medical care component of
               the Consumer Price Index ("CPI") plus two percent (2%), subject
               to a minimum increase of eight percent (8%) and a maximum
               increase of ten percent (10%).  Effective January 1, 2002, the
               capitation rate shall be the capitation rate for calendar year
               2001 increased by the medical care component of CPI plus two
               percent (2%), subject to a minimum increase of six percent (6%)
               and a maximum increase of ten percent

                                          -9-

<PAGE>

               (10%).  As used herein, "CPI" means the medical care component of
               the Consumer Price Index for all urban consumers, United States
               City Average, during the preceding twelve month period running
               from October 1 through September 30.

          (d)  CAPITATION ADJUSTMENT:  The capitation shall be adjusted to
               reflect the following factors:  age, sex, family status (e.g.,
               single, two individuals, family), product line, and variable
               office copayment.  The capitation amount paid to the Clinic for
               each product line shall be actuarially determined to reflect the
               anticipated utilization of services.  However, regardless of the
               foregoing, the Clinic agrees that it shall offer to the joint
               venture its "Best Price" as set forth in Article 6 of this
               Agreement.  Clinic reimbursement will be reviewed annually at the
               request of the Clinic to consider the impact on the capitation
               rate of new technology not reflected in the CPI, the effect of
               new insurance mandates, changes in plan design, and unexpected
               changes in applicable community standards of practice.
               Adjustments to the capitation rate will be negotiated if
               appropriate and, if the parties cannot agree upon an appropriate
               adjustment, the Governing Board shall determine the appropriate

                                          -10-

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               adjustment, if any.

          (e)  FEE SCHEDULE ADJUSTMENT:  The Clinic agrees to provide written
               notice to VHP of any increase in the fee schedule by December 1
               of each year, and any increase will become effective on the
               following January 1.

          (f)  CONTRACT TERM:  The contract shall have an initial term ("Initial
               Term" as defined in Section 7.1, herein) of three (3) years and
               may be renewed for an additional three (3) year term by mutual
               agreement; otherwise renewal shall be for one year terms unless
               written notice of termination is given at least 120 days prior to
               the end of the then current term. A party may terminate the
               contract at the end of the Initial Term if proper notice is
               given.

          (g)  CONTINUED ACCESS TO CARE:  The contract shall include a provision
               under which the Clinic agrees, if requested, to (i) extend
               continued services to all groups affected by a termination of a
               provider contract until the end of each such group's benefit year
               or as necessary to comply with state and federal law relating to
               accessibility of providers following contract termination; and
               (ii) accept reimbursement terms and other contract terms in
               effect prior to the termination during

                                          -11-

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               the period of any such extension.

                                 5.  PROFIT SHARING
                                 ------------------

     5.1  Underwriting losses of the Insured Products shall be the liability of
          the Underwriters.  Notwithstanding the above, fifty percent (50%) of
          the net profits relating to HMO products and fifty percent (50%) of
          the net profits relating to the POS products shall be paid to the
          Clinic as set forth in this Article 5.

     5.2  Net profit/loss of HMO products and POS products shall be separately
          calculated.  Net profit/loss of HMO products shall be calculated on an
          aggregate basis following the Initial Term of this Agreement as
          defined in Section 7.1 herein.  Notwithstanding the foregoing, net
          profit/loss of HMO products shall be determined on an annual basis,
          and interim profit-sharing shall occur as set forth in Sections 5.3
          and 5.4, below.  Net profit/loss of POS products shall be determined
          annually at the end of each calendar year during the term of this
          Agreement, and profit-sharing shall occur at the end of each such
          calendar year as set forth in Section 5.5, below.  A listing of HMO
          products and POS products is attached to this Agreement and
          incorporated herein as Attachment B.

     5.3  Aggregate net profit of HMO products shall be the sum

                                          -12-

<PAGE>

          of net profits and losses of VHP over the entire Initial Term of
          this Agreement. Such net profit/loss shall be determined by applying
          the same accounting principles applied in preparing VHP's December 31,
          1999 financial statement.  As further clarification, calculation of
          net profit/loss shall not take into account any adjustments to the
          reconciled purchase price as outlined in Section 4.4 of the Purchase
          and Sale Agreement, any profit sharing payments made pursuant to this
          Agreement, or any provision for the payment of taxes.  A party's share
          of aggregate net profit shall not include any investment income
          attributable to the other party's share of aggregate net profit.  A
          sample profit-sharing calculation is attached to this Agreement and
          incorporated herein as Attachment C. Notwithstanding actual
          administrative expenses incurred, total administrative expenses which
          may be charged against income in calculating net profit/loss of VHP
          shall be the lesser of:  (i) actual costs incurred by VHP; or (ii)
          eight and one-half percent (8 1/2%) of the gross premiums received for
          that benefit year by VHP.

     5.4  Notwithstanding that the aggregate net profit/loss of the HMO product
          is determined over the entire Initial Term of this Agreement, the
          Clinic is interested in sharing net profits with the Underwriters on
          an interim

                                          -13-

<PAGE>

          basis and the Underwriters are interested in recouping, on an interim
          basis, from the Clinic any profits shared for which loss carry backs
          indicate an overpayment was made.  Interim profit sharing and
          recoupment shall be as follows:

          (a)  Within 120 days following the end of the first Benefit Year, UWS
               shall determine the net profit or loss as described in Section
               5.2, above for that Benefit Year alone.  "Benefit Year" is
               defined as a calendar year beginning on January 1 and ending on
               December 31 of the same year for all years falling within the
               Initial Term of this Agreement.  If an aggregate net profit is
               present, UWS shall make available to the Clinic a line of credit,
               within 150 days following the end of the first Benefit Year,
               equal to the Clinic's fifty percent (50%) share of the aggregate
               net profit.  The Clinic may draw on the line of credit.  Any
               monies so drawn on by the Clinic shall herein be referred to as
               the "Balance Drawn".

          (b)  Within 120 days following the end of the second Benefit Year, UWS
               shall determine the aggregate net profit or loss as described in
               Section 5.2 above, for the first two Benefit Years, accounting
               for both loss carry forwards and loss carry backs.

               (i)  Within 150 days following the end of each

                                          -14-

<PAGE>

                    such Benefit Year, the amount of the line of credit shall be
                    adjusted so as to be equal to the Clinic's fifty percent
                    (50%) share of the aggregate net profit so calculated.

               (ii) If after such adjustment to the amount of the line of credit
                    the Balance Drawn by the Clinic exceeds the adjusted line of
                    credit ("Overdraft"), the Clinic shall repay to UWS the
                    amount of the Overdraft plus accruing interest.  Repayment
                    shall be in twelve equal installments beginning on the first
                    of the month 150 days following the end of the last Benefit
                    Year.  Interest on the monies owed by the Clinic shall
                    accrue at the prime rate, plus 100 basis points, as
                    determined by M & I Marshall & Ilsley Bank, Milwaukee,
                    Wisconsin, on the close of business on the last business day
                    of the month preceding when the first installment is due.
                    Interest shall accrue beginning on the first of the month
                    150 days following the end of the last Benefit Year.  The
                    Clinic may repay all or part of the Overdraft at any time.

          (c)  Within 180 days following the end of the third Benefit Year of
               the Initial Term, UWS shall determine the aggregate net profit or
               loss as

                                          -15-

<PAGE>

               determined in Section 5.2 above for all Benefit Years which
               comprise the Initial Term of this Agreement, accounting for
               both loss carry forwards and loss carry backs.

               (i)  If an aggregate net profit is present, UWS shall pay to the
                    Clinic, within 210 days following the end of the third
                    Benefit Year of the Initial Term, the Clinic's respective
                    fifty percent (50%) share of the aggregate net profit.  The
                    Clinic's share of such aggregate net profit shall be paid to
                    it by UWS first canceling the Balance Drawn by the Clinic,
                    up to the Clinic's share of such aggregate net profit.  If
                    after such cancellation, aggregate net profit remains to be
                    paid to the Clinic by UWS, an appropriate cash payment shall
                    be made by UWS to the Clinic.  If after such cancellation an
                    Overdraft remains to be paid by the Clinic on the line of
                    credit, the Clinic shall repay such Overdraft as set forth
                    in item (ii) below.

               (ii) If an aggregate net loss is present, the Clinic shall repay
                    UWS the Overdraft.  Repayment shall be within 210 days
                    following the end of the third Benefit Year of the

                                          -16-

<PAGE>

                    Initial Term.  Interest on the monies owed by the Clinic
                    shall accrue at the prime rate, plus 100 basis points, as
                    determined by M & I Marshall & Ilsley Bank, Milwaukee,
                    Wisconsin, on the close of business on the last business day
                    of the month preceding when repayment is due.  Interest
                    shall accrue beginning on the first of the month 210 days
                    following the end of the final Benefit Year of the Initial
                    Term.  The Clinic may repay all or part of the amount owed
                    at any time.

          (d)  If, after the Initial Term, this Agreement is renewed for an
               additional three year term or terms in accordance with Section
               7.1, aggregate net profit shall be shared on an interim basis as
               described in (a) and (b), above, with final reconciliation
               occurring following the third year of each such three year term
               as described in (c) above.  If this Agreement is renewed for one
               or more one-year terms, final reconciliation shall occur at the
               end of each such one-year term.

     5.5  Net profit/loss of POS products shall be determined as of the end of
          each calendar year during the term of this Agreement, and
          profit-sharing payments, if any, shall be paid to the Clinic within
          150 days following the end of each such calendar year as set forth
          below:

                                          -17-

<PAGE>

     (a)  The Net profit/loss of POS products shall equal the sum of (i) and
          (ii):

          (i)  UNDERWRITING PROFIT/LOSS.  Net underwriting profit/loss shall be
               calculated as net earned premium less the sum of incurred claims
               and administrative expenses.  Total administrative expenses used
               in calculating net underwriting profit/loss shall not exceed the
               Actual Cost incurred by the Underwriter pursuant to the
               administrative services agreements referenced in Section 4.2 of
               this Agreement.

          (ii) EXCESS LOSS REINSURANCE.  Net profit/loss of excess loss
               reinsurance provided by Blue Cross or an insurer affiliated with
               Blue Cross for each POS plan underwritten by VHP and offered
               through this joint venture shall be calculated as reinsurance
               premium paid to the reinsurer, less:  (i) claims paid plus; (ii)
               a reserve for claims reported but not yet paid, and claims
               incurred but not yet reported; and (iii) administrative expenses
               or fees related to the reinsurance policy.

     (c)  VHP shall pay fifty percent (50%) of annual net profit for the POS
          product to the Clinic subject to the following limitations:  (i) for
          calendar year 2000, the Clinic's share of profit may not exceed
          $100,000, nor may its share of loss exceed $100,000; (ii) for

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<PAGE>

          calendar year 2001, the Clinic's share of profit may not exceed
          $150,000, nor may its share of loss exceed $150,000; and (iii) for
          calendar year 2002, the Clinic's share of profit may not exceed
          $200,000, nor may its share of loss exceed $200,000.

                                  6.  EXCLUSIVITY
                                  ---------------

     6.1  During the Initial Term of this Agreement (as defined in Section 7.1
          herein) or any subsequent term(s), unless otherwise agreed by the
          Governing Board, (i) the Underwriters and UWS agree that they will not
          market any insured HMO or POS product within the Exclusive Area (as
          defined below) except through VHP; and (ii) the Clinic agrees that it
          will not participate in the provider network for any employer offering
          an insured HMO or POS product within the Exclusive Area except through
          VHP.  As used in this Article, "Exclusive Area" means the Wisconsin
          counties of Chippewa, Eau Claire or Dunn.

     6.2  Regardless of anything provided in Section 6.1 to the contrary, the
          Underwriters and the Clinic may participate in the offering of a
          competing insured HMO or POS product with respect to an employer which
          has multiple locations, one or more of which is located within the
          Exclusive Area, if the employer's headquarters are located outside the
          Exclusive Area;

                                          -19-

<PAGE>

          provided, however, that if the employer is the federal government or
          the State of Wisconsin, the insured HMO or POS product shall be
          offered only through the joint venture.

     6.3  The Clinic agrees to offer its Best Price to VHP for all products
          offered under this Agreement within the Exclusive Area and within the
          Wisconsin county of Barron.  As used herein, "Best Price" means a
          price that is equal to or lower than the price the Clinic accepts from
          any other non-governmental payor with respect to insured HMO and/or
          POS products. In the event the Clinic offers a price to any other
          payor that is less than the Best Price offered to the joint venture
          for like services, the lower price will also be extended to the joint
          venture and immediately and automatically become the new Best Price.

     6.4  The parties to this Agreement acknowledge that Blue Cross has an
          existing contract with the Clinic to serve as a provider for the Blue
          Cross "Quality Choice" POS product and agree that such contract does
          not violate the provisions of this Article 6.

     6.5  The parties to this Agreement acknowledge and agree that the
          provisions of this Article 6 are binding on those subsidiaries and
          affiliates of the Clinic existing on January 1, 1992, and shall be
          binding on later acquired or established subsidiaries or

                                          -20-

<PAGE>

          affiliates only if such entities signify in writing their intent to
          be bound.

                              7.  TERM AND TERMINATION
                              ------------------------

     7.1  The Initial Term of this Second Amended and Restated Joint Venture
          Agreement shall be for three years, commencing on January 1, 2000 and
          continuing in effect through December 31, 2002.  This Agreement may be
          renewed for an additional three year term or terms, commencing on
          January 1, 2003, by mutual written agreement of the parties; otherwise
          the joint venture shall automatically renew for one year terms unless
          written notice of termination is given at least 120 days prior to the
          end of the then current term.  This Agreement may be terminated at the
          end of the Initial Term if proper notice is given.

     7.2  Notwithstanding the above, if, in accordance with the Purchase and
          Sale Agreement, Clinic exercises its right to repurchase all
          outstanding shares of VHP stock from UWS at the end of the Initial
          Term of this Second Amended and Restated Joint Venture Agreement, or
          its termination, whichever is earlier, this Agreement shall terminate
          unless the parties mutually agree otherwise in writing. Additionally,
          in the event that a party substantially breaches any material term or
          condition of this Agreement, notice of the specific breach shall

                                          -21-

<PAGE>

          be given to the breaching party.  The breaching party shall have sixty
          (60) days to cure such breach.  In the event the breaching party fails
          to cure said breach, the non-breaching party shall have the right to
          terminate this Agreement on thirty (30) days prior written notice.

     7.3  Notwithstanding the termination of this Agreement, all provider and
          administrative services agreements entered into by the parties shall
          continue according to the provisions contained in those provider
          agreements until their scheduled termination date.

                                 8.  MISCELLANEOUS
                                 -----------------

     8.1  The parties agree to utilize their best efforts in carrying out their
          respective duties and obligations under this Agreement to ensure that
          the purposes of this undertaking are accomplished.

     8.2  In the event of a dispute between the parties relating to this
          Agreement, such dispute shall be resolved by arbitration in accordance
          with the rules of the American Arbitration Association.  The inability
          of the Governing Board to take action with regard to a particular
          matter due to an impasse shall not be treated as a dispute affording
          either party the right to demand arbitration to resolve such impasse.

                                          -22-

<PAGE>

     8.3  This Agreement supersedes all prior agreements, proposals, offers or
          letters of intent, including the prior joint venture agreements,
          relating to the subject matter hereof.  Any amendment to this
          Agreement must be in writing, executed by, and delivered to, each of
          the parties.

     8.4  In the event that a court, regulator, or administrative judge of
          competent jurisdiction declares any provision of this Agreement to be
          invalid or unenforceable, such declaration shall have no effect on the
          validity or enforceability of the remainder of this Agreement;
          provided, however, that the basic purposes of this Agreement may be
          achieved through the remaining valid provisions.

     8.5  The parties acknowledge that all material and information of a given
          party which has or will come into the possession of another party in
          connection with this Agreement consists of confidential and
          proprietary data.  Each party agrees to hold such material and
          information in strictest confidence, not to make use thereof other
          than for the performance of this Agreement, and not to release or
          disclose it to any third party other than for the performance of this
          Agreement.

     8.6  Failure by any party to insist upon compliance with any term or
          provision of this Agreement at any time or

                                          -23-

<PAGE>

          under any set of circumstances will not operate to waive or modify
          that provision or render it unenforceable at any other time.

     8.7  This Agreement shall be construed according to the laws of the State
          of Wisconsin.

     8.8  All notices required or permitted by this Agreement shall be sent to
          the following addresses, or to such other persons or locations
          indicated in writing by the parties:

          BLUE CROSS:
          Penny J. Siewert, Vice President of Regional Services
          N17 W24340 Riverwood Drive
          Waukesha, WI  53188

          UWS:
          Thomas R. Hefty, President
          401 West Michigan Street
          Milwaukee, WI 53203

          VHP:
          Norman L. Keller, President
          Valley Health Plan, Inc.
          2270 EastRidge Center
          Eau Claire, WI  54701

          CLINIC:
          Robert Downs, Executive Vice President
          Midelfort Clinic, Ltd., Mayo Health System
          1400 Bellinger Street
          P. O. Box 1510
          Eau Claire, WI  54702

     8.9  No party may assign its rights or delegate its duties under this
          Agreement without the prior written consent of the other parties.
          Such approved assignment or delegation shall inure to the benefit of
          the parties, their successors, and their permitted assigns or

                                          -24-

<PAGE>

          delegates.

     8.10 Each signatory hereto represents and warrants that his/her execution
          of this Agreement on behalf of his/her respective party has been duly
          authorized and approved by the parties' Board of Directors and/or
          shareholders (if legally required).

     IN WITNESS WHEREOF, the parties have caused this Agreement to be executed
by their respective representatives.

Attest:                       BLUE CROSS & BLUE SHIELD
                              UNITED OF WISCONSIN
---------------------

                              By:
                                  -------------------------
                              Title:
                                     ----------------------

Attest:                       UNITED WISCONSIN SERVICES, INC.

---------------------

                              By:
                                  -------------------------
                              Title:
                                     ----------------------

Attest:                       VALLEY HEALTH PLAN, INC.

---------------------

                              By:
                                  -------------------------
                              Title:
                                     ----------------------
                                          -25-

<PAGE>

Attest:                       MIDELFORT CLINIC, LTD., MAYO
                              HEALTH SYSTEM
---------------------

                              By:
                                  -------------------------
                              Title:
                                     ----------------------

ns01.c

                                          -26-

<PAGE>

                                    ATTACHMENT B

                                 HMO AND POS PLANS
                                 -----------------

HMO PLANS INCLUDE THE FOLLOWING PLANS:

     -    State of Wisconsin Plan
     -    Federal Employees Program
     -    Partner Plan
     -    Medicare Supplement Plan
     -    Medicaid Program
     -    BadgerCare Program
     -    Agricare Plan
     -    Agrihealth Plan
     -    Agrihealth Plan II

POS PLANS INCLUDE THE FOLLOWING PLANS:

All the accounts that have purchased the VHP POS product. These Plans are
uniquely identified by a group number in the 5000 series.  In the event the
block of numbers in this series becomes exhausted, however, it may be necessary
to select another series of numbers for future expansion.

                                          -27-

<PAGE>

                                    ATTACHMENT C

                         SAMPLE PROFIT-SHARING CALCULATION
                         ---------------------------------

     The following references lines of Report #2:  "State of Revenues, Expenses,
and Net Worth" which is filed annually by Valley Health Plan, Inc. with the
Wisconsin Office of the Commissioner of Insurance as of December 31.

     Line 29   Income (Loss)

     PLUS

     Line 30   Extraordinary Item

     MINUS

     Line 14   Incentive Pool and Withhold Adjustments
                    (only the joint venture profit-sharing portion)

     EQUALS

     TOTAL AMOUNT BEFORE IMPACT OF INTEREST ON WITHDRAWALS PLUS OR MINUS
     IMPACT OF INTEREST ON PREVIOUS YEARS WITHDRAWALS EQUALS TOTAL AMOUNT
     AFTER IMPACT OF INTEREST ON WITHDRAWALS

     DIVIDED BY 2

     EQUALS EACH PARTNER'S BEFORE TAX SHARE OF PROFIT

                                          -28-

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