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                                                                    Exhibit 10.6
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[LOGO OF FIRSTAR]              For Bank Use Only     Reviewed by
                               -------------------------------------------------
                               Due  DECEMBER 31, 2002
                                    --------------------
                               Customer                     Loan
                                         -----------------       ---------------

                          STAND-ALONE REVOLVING NOTE


$ 6,000,000.00                                      NOVEMBER 17, 2000
 -----------------------                            ----------------------------

     FOR VALUE RECEIVED, the undersigned borrower (the "Borrower"), promises to
pay to the order of FIRSTAR BANK, N.A. (the "Bank"), the principal sum of SIX
                    ------------------                                    ---
MILLION AND NO/100 Dollars ($6,000,000.00), payable 12/31/02.
------------------          -------------           --------

     The Bank will make advances to the Borrower from time to time up to the
aggregate amount of $6,000,000.00. The Borrower may, prior to the maturity date
                    -------------
or termination as described below, borrow, repay and reborrow such amount from
the Bank. Each advance shall be in the minimum amount of $5,000.


  1. Interest.

  The unpaid principal balance will bear interest at an annual rate equal to
  the prime rate announced by the Bank.


  The interest rate hereunder will be adjusted each time that the prime rate
  changes.


  2. Payment Schedule.


  Interest is payable beginning DECEMBER 31, 2000, and on the same date of each
  CONSECUTIVE month thereafter (except that if a given month does not have such
  a date, the last day of such month), plus a final interest payment with the
  final payment of principal.

  3. Paid-in-Full Period. [_] If checked here, all revolving loans under this
Note must be paid in full for a period of at least     consecutive days during
                                                   ---
each fiscal year.

  4. Closing Fee. [_] If checked here, the Borrower will pay the Bank a one-time
closing fee of $ n/a contemporaneously with execution of this Note. This fee
               -----
is in addition to all other fees, expenses and other amounts due hereunder.

  5. Late Payment Fee. Subject to applicable law, if any payment is not made on
or before its due date, the Bank may collect a delinquency charge of 0.00% of
                                                                     -----
the unpaid amount. Collection of the late payment fee shall not be deemed to be
a waiver of the Bank's right to declare a default hereunder.

  6. Calculation of Interest. Interest will be computed for the actual number of
days principal is unpaid, using a daily factor obtained by dividing the stated
interest rate by 360.

  7. Default Interest Rate. Principal amounts remaining unpaid after the
maturity thereof, whether at fixed maturity or by reason of acceleration of
maturity, shall bear interest from and after maturity until paid at a rate of 3%
per annum plus the rate otherwise payable hereunder.

  8. Maximum Rate. In no event will the interest rate hereunder exceed that
permitted by applicable law. If any interest or other charge is finally
determined by a court of competent jurisdiction to exceed the maximum amount
permitted by law, the interest or charge shall be reduced to the maximum
permitted by law, and the Bank may credit any excess amount previously collected
against the balance due or refund the amount to the Borrower.

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  9. Financial Information. The Borrower will (i) maintain accounting records in
accordance with generally recognized and accepted principles of accounting
consistently applied throughout the accounting periods involved; (ii) provide
the Bank with such information concerning its business affairs and financial
condition (including insurance coverage) as the Bank may reasonably request; and
(iii) without request, provide the Bank with annual financial statements
prepared by an accounting firm acceptable to the Bank within 120 days of the end
of each fiscal year.

  10. Credit Balances; Setoff. As additional security for the payment of the
obligations described in this Note or any document securing or related to the
loan evidenced by this Note (collectively the "Loan Documents"), and any other
obligations of the Borrower to the Bank of any nature whatsoever (collectively
the "Obligations"), the Borrower hereby grants to the Bank a security interest
in, a lien on and an express contractual right to set off against all depository
account balances, cash and any other property of the Borrower now or hereafter
in the possession of the Bank and the right to refuse to allow withdrawals from
any account (collectively "Setoff"). The Bank may, at any time upon the
occurrence of a default hereunder (notwithstanding any notice requirements or
grace/cure periods under this or other agreements between the Borrower and the
Bank) Setoff against the Obligations whether or not the Obligations (including
future installments) are then due or have been accelerated, all without any
advance or contemporaneous notice or demand of any kind to the Borrower, such
notice and demand being expressly waived.

  11. Advances and Paying Procedure. The Bank is authorized and directed to
credit any of the Borrower's accounts with the Bank (or to the account the
Borrower designates in writing) for all loans made hereunder, and the Bank is
authorized to debit such account or any other account of the Borrower with the
Bank for the amount of any principal or interest due or other amount due
hereunder on the due date with respect thereto.

  12. Defaults. Notwithstanding any cure periods described below, the Borrower
shall immediately notify the Bank in writing when the Borrower obtains
knowledge of the occurrence of any default specified below. Regardless of
whether the Borrower has given the required notice, the occurence of one or more
of the following shall constitute a default:

  (a) Nonpayment. The Borrower shall fail to pay (i) any interest due on this
      Note or any fees, charges, costs or expenses under the Loan Documents by 5
      days after the same becomes due; or (ii) any principal amount of this Note
      when due.

  (b) Nonperformance. The Borrower or any guarantor of the Borrower's
      Obligations to the Bank ("Guarantor") shall fail to perform or observe any
      agreement, term, provision, condition, or covenant (other than a default
      occurring under (a), (c), (d), (e), (f) or (g) of this paragraph 12)
      required to be performed or observed by the Borrower or any Guarantor
      hereunder or under any other Loan Document or other agreement with or in
      favor of the Bank.

  (c) Misrepresentation. Any financial information, statement, certificate,
      representation or warranty given to the Bank by the Borrower or any
      Guarantor (or any of their representatives) in connection with entering
      into this Note or the other Loan Documents and/or any borrowing
      thereunder, or required to be furnished under the terms thereof, shall
      prove untrue or misleading in any material respect (as determined by the
      Bank in the exercise of its judgment) as of the time when given.

  (d) Default on Other Obligations. The Borrower or any Guarantor shall be in
      default under the terms of any loan agreement, promissory note, lease,
      conditional sale contract or other agreement, document or instrument
      evidencing, governing or securing any indebtedness owing by the Borrower
      or any Guarantor to the Bank or any indebtedness in excess of $10,000
      owing by the Borrower to any third party, and the period of grace, if any,
      to cure said default shall have passed.

  (e) Judgments. Any judgment shall be obtained against the Borrower or any
      Guarantor which, together with all other outstanding unsatisfied judgments
      against the Borrower (or such Guarantor), shall exceed the sum of $10,000
      and shall remain unvacated, unbonded or unstayed for a period of 30 days
      following the date of entry thereof.

  (f) Inability to Perform; Bankruptcy/Insolvency. (i) The Borrower or any
      Guarantor shall die or cease to exist; or (ii) any Guarantor shall attempt
      to revoke any guaranty of the Obligations described herein, or any
      guaranty becomes unenforcable in whole or in part for any reason; or (iii)
      any bankruptcy, insolvency or receivership proceedings, or an assignment
      for the benefit of creditors, shall be commenced under any Federal or
      state law by or against the Borrower or any Guarantor; or (iv) the
      Borrower or any Guarantor shall become the subject of any out-of-court
      settlement with its creditors; or (v) the Borrower or any Guarantor is
      unable or admits in writing its inability to pay its debts as they mature.

  13. Termination of Loans; Additional Bank Rights. Upon the occurence of any of
the events identified in paragraph 12, the Bank may at any time (notwithstanding
any notice requirements or grace/cure periods under this or other agreements
between the Borrower and the Bank); (ii) Setoff; and/or (iii) take such other
steps to protect or preserve the Bank's interest in any collateral, including
without limitation, notifying account debtors to make payments directly to the
Bank, advancing funds to protect any collateral and insuring collateral at the
Borrower's expense; all without demand or notice of any kind, all of which are
hereby waived.

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  14. Acceleration of Obligations. Upon the occurrence of any of the events
identified in paragraph 12(a) through 12(e) and the passage of any applicable
cure periods, the Bank may at any time thereafter, by written notice to the
Borrower, declare the unpaid principal balance of any Obligations, together with
the interest accrued thereon and other amounts accrued hereunder and under the
other Loan Documents, to be immediately due and payable; and the unpaid balance
shall thereupon be due and payable, all without presentation, demand, protest or
further notice of any kind, all of which are hereby waived, and notwithstanding
anything to the contrary contained herein or in any of the other Loan Documents.
Upon the occurrence of any event under paragraph 12(f), the unpaid principal
balance of any Obligations, together with all interest accrued thereon and other
amounts accrued hereunder and under the other Loan Documents, shall thereupon be
immediately due and payable, all without presentation, demand, protest or notice
of any kind, all of which are hereby waived, and notwithstanding anything to the
contrary contained herein or in any of the other Loan Documents. Nothing
contained in paragraph 12 or 13 of this paragraph shall limit the Bank's right
to Setoff as provided in this Note.

  15. Collateral. This Note is secured by any and all security interests,
pledges, mortgages or liens now or hereafter in existence granted to the Bank to
secure indebtedness of the Borrower to the Bank (unless prohibited by law),
including, without limitation, as described in the following documents:
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 16. Guaranties. This Note is guaranteed by
                                            ------------------------------------
RICHARD B MAZESS
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  17. Additional Bank Rights. Without affecting the liability of any Borrower,
endorser, surety or guarantor, the Bank may, without notice, renew or extend the
time for payment, accept partial payments, release or impair any collateral
security for the payment of this Note, or agree not to sue any party liable on
it.

  18. Warranties. The Borrower makes the following warranties: (A) If the
Borrower is a corporation or partnership, it is a validly existing corporation
or partnership (as applicable), in good standing under the laws of its state of
organization, and has all requisite power and authority, corporate or otherwise,
and possesses all licenses necessary, to conduct its business and own its
properties. (B) The execution, delivery and performance of this Note and all
other Loan Documents (i) are within the Borrower's power; (ii) have been duly
authorized by proper corporate or partnership action (as applicable); (iii) do
not require the approval of any governmental agency; and (iv) will not violate
any law, agreement or restriction by which the Borrower is bound. (C) This Note
and the other Loan Documents are the legal, valid and binding obligations of the
Borrower, enforceable against the Borrower in accordance with their terms.

  19. Waivers; Relationship to Other Documents. All Borrowers, endorsers,
sureties and guarantors waive presentment, protest, demand, and notice of
dishonor. The warranties, covenants and other obligations of the Borrower (and
rights and remedies of the Bank) in this Note and all related documents are
intended to be cumulative and to supplement each other.

  20. Expenses and Attorneys' Fees. The Borrower will reimburse the Bank and any
participant in the Obligations ("Participant") for all attorneys' fees and all
other costs, fees and out-of-pocket disbursements (including fees and
disbursements of both inside counsel and outside counsel) incurred by the Bank
or any Participant in connection with the preparation, execution, delivery,
administration, defense and enforcement of this Note or any of the other Loan
Documents, including fees and costs related to any waivers or amendments with
respect thereto (examples of costs and fees include but are not limited to fees
and costs for filing, perfecting or confirming the priority of the Bank's lien,
title searches or insurance, appraisals, environmental audits and other reviews
related to the Borrower, any collateral or the loans, if requested by the Bank).
The Borrower will also reimburse the Bank and any Participant for all costs of
collection before and after judgement, and the costs of preservation and/or
liquidation of any collateral (including fees and disbursements of both inside
and outside counsel).

  21. Applicable Law and Jurisdiction; Interpretation; Joint Liability. This
Note and all other Loan Documents shall be governed by and interpreted in
accordance with the internal laws of the State of Wisconsin, except to the
extent superseded by Federal law. Invalidity of any provisions of this Note
shall not affect any other provision. THE BORROWER HEREBY CONSENTS TO THE
EXCLUSIVE JURISDICTION OF ANY STATE OR FEDERAL COURT SITUATED IN THE COUNTY OR
FEDERAL JURISDICTION OF THE BANK'S BRANCH WHERE THE LOAN WAS ORIGINATED, AND
WAIVES ANY OBJECTION BASED ON FORUM NON CONVENIENS, WITH REGARD TO ANY ACTIONS,
CLAIMS, DISPUTES, OR PROCEEDINGS RELATING TO THIS NOTE, THE COLLATERAL, ANY
OTHER LOAN DOCUMENT, OR ANY TRANSACTIONS ARISING THEREFROM, OR ENFORCEMENT
AND/OR INTERPRETATION OF ANY OF THE FOREGOING. Nothing herein shall affect the
Bank's rights to serve process in any manner permitted by law, or limit the
Bank's right to bring proceedings against the Borrower in the competent courts
of any other jurisdiction or jurisdictions. This Note, the other Loan Documents
and any amendments hereto (regardless of when executed) will be deemed effective
and accepted only upon the Bank's receipt of the executed originals thereof. If
there is more than one Borrower, the liability of the Borrowers shall be joint
and several, and the reference to "Borrower" shall be deemed to refer to all
Borrowers.

  22. Copies; Entire Agreement; Modification. The Borrower hereby acknowledges
the receipt of a copy of this Note and all other Loan Documents.

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  IMPORTANT: READ BEFORE SIGNING. THE TERMS OF THIS AGREEMENT SHOULD BE READ
CAREFULLY BECAUSE ONLY THOSE TERMS IN WRITING ARE ENFORCEABLE. NO OTHER TERMS OR
ORAL PROMISES NOT CONTAINED IN THIS WRITTEN CONTRACT MAY BE LEGALLY ENFORCED.
THE TERMS OF THIS AGREEMENT MAY ONLY BE CHANGED BY ANOTHER WRITTEN AGREEMENT.
THIS NOTICE SHALL ALSO BE EFFECTIVE WITH RESPECT TO ALL OTHER CREDIT AGREEMENTS
NOW IN EFFECT BETWEEN BORROWER AND THE BANK. A MODIFICATION OF ANY OTHER CREDIT
AGREEMENTS NOW IN EFFECT BETWEEN BORROWER AND THE BANK, WHICH OCCURS AFTER
RECEIPT BY BORROWER OF THIS NOTICE, MAY BE MADE ONLY BY ANOTHER WRITTEN
INSTRUMENT. ORAL OR IMPLIED MODIFICATIONS TO SUCH CREDIT AGREEMENTS ARE NOT
ENFORCEABLE AND SHOULD NOT BE RELIED UPON.

  23. Waiver of Jury Trial. THE BORROWER AND THE BANK HEREBY JOINTLY AND
SEVERALLY WAIVE ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY ACTION OR PROCEEDING
RELATING TO ANY OF THE LOAN DOCUMENTS, THE OBLIGATIONS THEREUNDER, ANY
COLLATERAL SECURING THE OBLIGATIONS, OR ANY TRANSACTION ARISING THEREFROM OR
CONNECTED THERETO. THE BORROWER AND THE BANK EACH REPRESENTS TO THE OTHER THAT
THIS WAIVER IS KNOWINGLY, WILLINGLY AND VOLUNTARILY GIVEN.

  24. Attachments. All documents attached hereto, including any appendices,
schedules, riders, and exhibits to this Stand-Alone Revolving Note, are hereby
expressly incorporated by reference.

(Individual Borrower)        BONE CARE INTERNATIONAL, INC.
                             ---------------------------------------------------
                             Borrower Name (Organization)

                  (SEAL)     a WISCONSIN Corporation
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Borrower Name      N/A       By /s/ Robert A. Beckman
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                  (SEAL)     Name and Title Robert A. Beckman, Acting VP Finance
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                             By
                             ---------------------------------------------------

Borrower Name      N/A       Name and Title
------------------------     ---------------------------------------------------


Borrower Address: ONE SCIENCE CT. MADISON, WI 53711-1055
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Borrower Telephone No.: 608-236-2500
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ACKNOWLEDGE:
FIRSTAR BANK, N.A.
By: /s/ Douglas A. Rahn, Jr., V.P.
Douglas A. Rahn, Jr., Vice President

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