Exhibit 10.6

                   SECURITIES PURCHASE AGREEMENT

          This Securities Purchase Agreement (the "AGREEMENT"), dated
as of October 11, 1999 is entered into by and between The State of
Wisconsin Investment Board, an independent state agency organized
under the laws of Wisconsin, with an address at 121 East Wilson
Street, 2nd Floor, Madison, Wisconsin 53707-7842, Attn: Investment
Director, Small Cap Stocks (the "PURCHASER") and Bone Care
International, Inc., a Wisconsin corporation with an address of One
Science Court, Madison Wisconsin 53711 (the "COMPANY").

          The Company is offering for sale, to the Purchaser and to
certain other parties (the "OTHER PURCHASERS"), and the Purchaser and
the Other Purchasers have agreed to purchase, on substantially the
same price terms as contained herein, in the aggregate, not more than
(1,385,000) shares of the Company's common stock, no par value per
share (the "COMMON STOCK").  The Company has offered for sale, and the
Purchaser has agreed to purchase 1,052,058 shares (the "SHARES") of
fully registered Common Stock on the terms and conditions herein
provided.  In connection herewith, the Company and the Purchaser
hereby agree as follows:

     1.   PURCHASE AND SALE OF SHARES.  Upon the basis of the
representations and warranties and subject to the terms and conditions
set forth herein, the Company agrees to issue and sell the Shares to
the Purchaser on the Closing Date (as herein defined) at a per share
purchase price equal to $9.02 (the "PER SHARE PURCHASE PRICE," and the
aggregate purchase price of all of the Shares being referred to herein
as the "PURCHASE PRICE") and, upon the basis of representations and
warranties and subject to the terms and conditions set forth herein,
the Purchaser agrees to purchase the Shares from the Company on the
Closing Date at the Purchase Price.

          Notwithstanding the foregoing, in the event that the Company
sells any shares (or securities that may be converted into or
exchanged for shares) of Common Stock in an original issuance (not
shares traded on the Nasdaq National Market in the aftermarket) for
less per share than the Per Share Purchase Price at any time during
the sixty day period commencing on the Closing Date (except for shares
issued pursuant to stock options), the Company shall have the
obligation to promptly notify and pay the Purchaser:   (x) the
aggregate difference between (i) the Per Share Price of the Shares and
(ii) the per share price of such additional shares of the Company's
Common Stock (or securities that may be converted into or exchanged
for shares of Common Stock) so sold, MULTIPLIED by (y) the number of
Shares purchased hereunder, payable,  at the Company's option, in
either cash or additional shares of the Company's Common Stock.  If
the Company elects to pay in Common Stock, the Common Stock shall be
valued at the price at which the Company sells any such shares (or
securities that may be converted into or exchanged for shares) of
Common Stock and will be payable within five (5) days of such other
sale.

     2.   CLOSING.  The closing of the purchase and sale of the Shares
(the "OFFERING") shall take place, on the first business day following
the satisfaction of the conditions set forth in Paragraph 6 below, as
coordinated by the parties, or on such other date or at such other
time and place as the Company and the Purchaser may agree upon (such
time and date of the closing being referred to herein as the "CLOSING
DATE").  Upon payment of the Purchase Price in full in immediately
available funds by or on behalf of the Purchaser to the Company by
wire transfer to an account specified by the Company to the Purchaser
prior to the Closing Date, the Company will promptly cause its
transfer agent to deliver to the Purchaser certificates representing
the shares of Common Stock in such denominations and registered in
such names as the Purchaser shall have requested prior to the Closing
Date.  The Company shall provide facsimile copies of the certificates
to the Purchaser on the Closing Date.

     3.   REPRESENTAIONS AND WARRANTIES OF THE COMPANY.  The Company
represents and warrants, as of the date hereof and as of the Closing
Date, as follows:

          (a)  no consent, approval, authorization or order of any
     court, governmental agency or body or arbitrator having
     jurisdiction over the Company or any of the Company's affiliates
     is required for the execution of this Agreement or the sale of
     the Shares to the Purchaser, except as required by the Nasdaq
     Stock Market;

          (b)  neither the sale of the Shares nor the performance of
     the Company's other obligations pursuant to this Agreement will
     violate, conflict with, result in a breach of, or constitute a
     default (or an event that, with the giving of notice or the
     lapse of time or both, would constitute a default or trigger any
     right of a third party to acquire equity interests in the
     Company or cause mandatory adjustment of the price at which an
     outstanding security of the Company is convertible into Common
     Stock) under (i) the Articles of Incorporation or the bylaws of
     the Company, (ii) any decree, judgment, order or determination
     of any court, governmental agency or body, or arbitrator having
     jurisdiction over the Company or any of the Company's properties
     or assets, (iii) any law, treaty, rule or regulation applicable
     to the Company (other than the federal securities laws,
     representations and warranties with respect to which are made by
     the Company, or the requirements of the Nasdaq Stock Market),
     (iv) the terms of any bond, debenture, note or other evidence of
     indebtedness, or any agreement, stock option or similar plan by
     which the Company is bound or to which any property of the
     Company is subject, in any event above, which violation,
     conflict or breach would have a material adverse effect on the
     Company.

          (c)  the Company has taken all corporate action required to
     authorize the execution and delivery of this Agreement and the
     performance of its obligations hereunder and will use the
     proceeds of sale as described in the Registration Statement;

          (d)  the Company has duly authorized the issuance of the
     Shares and, when issued and delivered to and paid for by the
     Purchaser in accordance with the terms hereof, the Common Stock
     will be duly and validly issued, fully paid and non-assessable
     (except to the extent that such Shares are assessable as
     provided in Section 180.0622 of the Wisconsin Business
     Corporation Law) and will not constitute "restricted securities"
     within the meaning of Rule 144(a)(3) promulgated under the
     Securities Act of 1933, as amended (the "ACT");

          (e)  the Company's Prospectus dated October 6, 1999
     included in the Company's Registration Statement, the Company's
     Form 10  (File No. 0-27854), as amended and the Company's Annual
     Report on Form 10-K for its Fiscal Year ended June 30, 1999
     (collectively, the "DISCLOSURE DOCUMENTS") have been delivered
     or been made available to Purchaser and, as of the date of each
     such respective document included therein and when considered as
     of today together and with this Agreement, such Disclosure
     Documents do not contain any untrue statement of a material fact
     or omit to state a material fact required to be stated therein
     or necessary to make the statements therein not misleading in
     light of the circumstances in which they were made with respect
     to the Company;

          (f)  the Company's financial statements for the year ended
     June 30, 1999, included in the Disclosure Documents comply in
     all material respects with the applicable requirements of the
     Securities Exchange Act of 1934, as amended, and have been
     prepared, and fairly present in all material respects the
     consolidated financial condition, results of operations and cash
     flows of the Company and its subsidiaries at the respective
     dates and for the respective periods indicated, in accordance
     with generally accepted accounting principles consistently
     applied throughout such periods (except as noted therein);

          (g)  except as set forth in the Disclosure Documents or
     pursuant to this Agreement, since June 30, 1999 (i) the Company
     has not incurred any material liabilities, direct or contingent,
     except in the ordinary course of business, and (ii) there has
     been no material adverse change in the properties, business,
     results of operations of financial condition of the Company;

        the Company's Registration Statement on Form S-1 (No. 333-
   87789), as amended, has been declared effective by the
   Securities and Exchange Commission ("COMMISION") (including all
   exhibits thereto and all information and documents incorporated
   by reference therein, the "REGISTRATION STATEMENT") and includes
   the registration of the original issuance of the Shares
   purchased by the Purchaser pursuant to this Agreement;


        the Company has all necessary patent and other license
   rights to conduct its business as it is now being conducted and
   as described in the Company's  Prospectus.  The Company has no
   knowledge of any material infringement by it of patent or other
   licensing rights of others or of any claim made or threatened
   against the Company in regard to patent or other licensing
   rights; and

        (j)  as of August 31, 1999 (and without giving effect to
   the sale of Shares of Common Stock hereunder), the Company had
   a total of 10,173,396 shares of Common Stock issued and
   outstanding, approximately 548,638 shares of Common Stock were
   subject to outstanding options granted under the Company's 1996
   Stock Option Plan or Incentive Stock Option Plan; approximately
   437,850 shares of Common Stock were reserved for future grant
   under the Company's 1996 Stock Option Plan; and there will be no
   changes in these numbers prior to the Closing Date except as a
   result of shares issued in connection with the conversion or
   exchange of any securities of the Company or stock options
   granted under or shares issued under any existing stock option
   plan or other existing employee bonus or existing incentive plan
   of the Company, or shares issued to Other Purchasers as
   contemplated by the Registration Statement.


   4.   REPRESENTATIONS AND WARRANTIES OF THE PURCHASER.  The
Purchaser represents and warrants, as of the date hereof and as of the
Closing Date, as follows:

        (a)  no consent, approval, authorization or order of any
   court, governmental agency or body or arbitrator having
   jurisdiction over the Purchaser is required for the execution of
   this Agreement or the purchase of the Shares by the Purchaser;

        (b)  neither the purchase of the Shares nor the performance
   of the Purchaser's other obligations pursuant to this Agreement
   will violate, conflict with, result in a breach of, or
   constitute a default under (i) the charter documents of the
   Purchaser; (ii) any decree, judgment, order or determination of
   any court, governmental agency or body, or arbitrator having
   jurisdiction over the Purchaser or any of the Purchaser's
   properties or assets; (iii) any law, treaty, rule or regulation
   applicable to the Purchaser; or (iv) the terms of any bond,
   debenture, note or other evidence of indebtedness, or any
   agreement, stock option or similar plan by which the Purchaser
   is bound or to which any property of the Purchaser is subject,
   in any event above, which violation, conflict or breach would
   have a material adverse effect on the Purchaser;

        (c)  the Purchaser has taken all corporate action required
   to authorize the execution and delivery of this Agreement and
   the performance of its obligations hereunder; and

        (d)  as of the date hereof, the Purchaser beneficially owns
   800,000 shares of Common Stock.

   5.   STOCK OPTIONS.      The Board of Directors has approved the
Company entering into this Agreement.  The Company agrees to take
action not later than November 17, 1999, an amendment to its bylaws,
to provide that the Company, without the approval of the owners of a
majority of the Common Stock, shall not grant any stock options at
less than the closing market price on the date of grant or reduce the
price of any options which were granted as a non-qualified stock
option under any of the Company's existing or future stock option
plans, PROVIDED, HOWEVER, that the foregoing would not preclude the
Company from issuing new, lower priced options issued from a stock
option plan to persons holding higher priced options from such plan;
PROVIDED, that if such new lower priced options were granted in
exchange for such higher priced options, the higher priced options
would be canceled or surrendered and not available for re-grant under
such stock option plan.

   6.   ONDITIONS OF CLOSING.  The obligations of each party
hereunder shall be subject to:

        (a)  The accuracy in all material respects of the
   representations and warranties of the other party hereto as of
   the date hereof and as of the Closing Date, as if such
   representations and warranties had been made again on and as of
   the Closing Date;

        (b)  The performance in all material respects by the other
   party of its obligations hereunder which must be performed prior
   to the Closing Date;

        (c)  the Registration Statement shall have been declared
   effective and no stop order suspending the effectiveness of the
   Registration Statement shall have been issued;

        (d)  The Purchaser shall have received a legal opinion of
   counsel to the Company substantially in the form attached hereto
   as EXHIBIT A.

   6.   INDEMNIFICATION.

        (a)  The Company agrees to indemnify and hold harmless the
   Purchaser, each person, if any, who controls the Purchaser
   within the meaning of Section 15 of the Act and each officer,
   director, employee and agent of the Purchaser and of any such
   controlling person against any and all liabilities, claims,
   damages or expenses whatsoever, as incurred arising out of or
   resulting from any breach (or, in the case of a third person
   claim, any alleged breach) or other violation of any
   representation, warranty, covenant, or undertaking by the
   Company contained in this Agreement, and the Company will
   reimburse the Purchaser for its reasonable legal and other
   expenses (including the reasonable cost of any investigation and
   preparation, and including the reasonable fees and expenses of
   counsel) incurred in connection therewith.

        (b)  The Purchaser agrees to indemnify and hold harmless
   the Company, each person, if any, who controls the Company
   within the meaning of Section 15 of the Act and each officer,
   director, employee and agent of the Company and of any such
   controlling person against any and all liabilities, claims,
   damages or expenses whatsoever, as incurred arising out of or
   resulting from any breach (or, in the case of a third person
   claim, any alleged breach) or other violation of any
   representation, warranty, covenant, or undertaking by the
   Purchaser contained in this Agreement, and the Purchaser will
   reimburse the Company for its reasonable legal and other
   expenses (including the reasonable cost of any investigation and
   preparation, and including the reasonable fees and expenses of
   counsel) incurred in connection therewith.

   7.   SURVIVAL OF REPRESENTATIONS AND WARRANTIES.  The respective
agreements, representations, warranties, indemnities and other
statements made by or on behalf of each party hereto pursuant to this
Agreement, as of the date they were made, shall, unless otherwise
specified, survive until the third anniversary of the Closing Date and
shall expire thereafter.

   8.   MISCELLANEOUS.

        (a)  This Agreement may be executed in one or more
   counterparts and such counterparts shall constitute but one and
   the same agreement and authorized signatures may be evidenced to
   the other party by facsimile copies thereof, provided that the
   originally signed signature page of any party is provided to the
   other party within two business days after the original
   execution.

        (b)  This Agreement shall inure to the benefit of and be
   binding upon the parties hereto.  This Agreement shall not be
   assignable by any party hereto without the prior written consent
   of the other party hereto and no other person shall have any
   right or obligation hereunder.  Without limiting the foregoing,
   the rights of Purchaser set forth in Paragraph 1 shall not be
   transferable to subsequent purchasers of the Shares.  Any
   assignment contrary to the terms hereof shall be null and void
   and of no force or effect.

        (c)  This Agreement contains the entire agreement between
   the parties with respect to the subject matter hereof and
   supersedes any prior agreements or understandings, whether
   written or oral, between the parties respecting such subject
   matter.

        (d)  If within 60 days of the Closing Date hereof the
   Company enters into or is a party to any agreement to issue
   additional equity securities (or securities convertible or
   exchangeable therefor), the Company shall promptly provide
   notice of such agreement to the Purchaser, together with a copy
   of such agreement, except for any grant of options to purchase
   Common Stock pursuant to the Company's 1996 Stock Option Plan.

   10.  GOVERNING LAW.  This Agreement shall be governed by the
internal laws of the State of Wisconsin.


   IN WITNESS WHEREOF, the parties have entered into this Agreement
as of the date first set forth above.

                  BONE CARE INTERNATIONAL INC.


                  By:  /s/ Charles W. Bishop
                       -----------------------------------
                  Name:     Charles W. Bishop, Ph.D.
                  Title:    President and Chief Executive Officer


                  THE STATE OF WISCONSIN INVESTMENT BOARD


                  By:   /s/ John F. Nelson
                       -----------------------------------
                  Name:     John F. Nelson,
                  Title:    Investment Director

                                           Exhibit A



                         October 12, 1999



State of Wisconsin Investment Board
Lake Terrace
121 East Wilson
Madison, Wisconsin  53707

        Re:  Bone Care International, Inc.
               1,052,058 Shares of Common Stock

Ladies and Gentlemen:

        We address this opinion to you as the purchaser (the
"Purchaser") from Bone Care International, Inc., a Wisconsin
corporation (the "Company"), of 1,052,058 shares (the "Shares") of
common stock, without par value (the "Common Stock"), of the Company.

        As counsel for the Company, we have, among other things,
participated with officers and other representatives of the Company,
including its independent public accountants, in the preparation of
the Company's Registration Statement on Form S-1 (Registration No.
333-87789) and Amendment No. 1 thereto, filed on September 24, 1999
and October 8, 1999, respectively, with the Securities and Exchange
Commission (the "SEC") under the Securities Act of 1933, as amended
(the "Securities Act"), which registration statement became effective
on October 6, 1999.  Such registration statement, as so amended
(including the information contained in the form of prospectus filed
with the SEC pursuant to Rule 424(b) under the Securities Act which
is deemed by Rule 430A under the Securities Act to be a part of such
registration statement as of the time it was declared effective), is
hereinafter called the "Registration Statement."  The Company's
Prospectus dated October 6, 1999, as filed with the SEC on October 12,
1998 pursuant to Rule 424(b) under the Securities Act, is hereinafter
called the "Prospectus."

        This will advise you that in the opinion of the undersigned:

   1.   The Registration Statement has been declared effective by
the SEC under the Securities Act.  To our knowledge, no stop order
suspending the effectiveness of the Registration Statement has been
issued under the Securities Act and no proceedings for such purpose
have been instituted or are being threatened by the SEC.  The
Prospectus has been filed with the SEC pursuant to Rule 424(b) under
the Securities Act within the time period required by such Rule.

   2.   The Shares will not constitute "restricted securities" within the
meaning of Rule 144(a)(3) promulgated under the Securities Act.

   3.   No consent, approval, authorization or other order of, or
registration or filing with, any court or other governmental authority
or agency is required for the Company's issuance and sale of the
Shares, except as required under the Securities Act, applicable state
securities or Blue Sky laws or by The Nasdaq Stock Market.

        For the purpose of rendering the foregoing opinions, we have
relied, as to various questions of fact material to such opinions,
upon certificates of officers of the Company.  We also have examined
originals, or copies of originals certified to our satisfaction, of
such agreements, documents, certificates and other statements of
governmental officials and other instruments, have examined such
questions of law and have satisfied ourselves as to such matters of
fact as we have considered relevant and necessary as a basis for the
foregoing opinions.  We have assumed the authenticity of all documents
submitted to us as originals, the genuineness of all signatures, the
legal capacity of all natural persons and the conformity with the
original documents of any copies thereof submitted to us for our
examination.

        Any opinion or statement herein which is expressed to be "to
our knowledge" or is otherwise qualified by words of like import means
that the lawyers currently practicing law with this Firm who have had
an active involvement in the preparation of the Registration Statement
or the Prospectus, or who have had a significant ongoing
responsibility in representing the Company during the last 12 months,
have no current conscious awareness of any facts or information
contrary to such opinion or statement.

        This opinion letter is limited to the federal laws of the
United States of America.  We express no opinion as to matters
relating to state securities or Blue Sky laws.  We assume no
obligation to update or supplement this opinion letter to reflect any
facts or circumstances which may hereafter come to our attention with
respect to the opinions and statements expressed above, including any
changes in applicable law which may hereafter occur.

        This opinion letter is being delivered solely for the
benefit of the person to whom it is addressed; accordingly, it may not
be quoted, filed with any governmental authority or other regulatory
agency or otherwise circulated or utilized for any other purpose
without our prior written consent.

         Very truly yours,











                         September 24, 1999



Bone Care International, Inc.
One Science Court
Madison, Wisconsin  53711

Ladies and Gentlemen:

   We have acted as special Wisconsin counsel to Bone Care
International, Inc., a Wisconsin corporation (the "Company"), in
connection with the Registration Statement on Form S-1 (the
"Registration Statement") filed by the Company with the Securities and
Exchange Commission under the Securities Act of 1933, as amended,
relative to the registration of up to 1,500,000 shares of Common
Stock, no par value (the "Shares"), of the Company to be offered by
the Company.

   We are familiar with the Articles of Amendment and Restated
Articles of Incorporation, as amended, and the By-Laws of the Company
and the proceedings to date with respect to the proposed offering and
sale of the Shares.  In this connection, we have examined originals
or copies of originals certified to our satisfaction, of such
documents, certificates and records, have examined such questions of
law and have satisfied ourselves as to such matters of fact as we have
considered relevant and necessary as a basis for the opinions set
forth herein.  We have assumed the authenticity of all documents
submitted to us as originals, the genuineness of all signatures, the
legal capacity of all natural persons and the conformity with the
original documents of any copies thereof submitted to us for our
examination.

   Based on the foregoing, we are of the opinion that:

   1.   The Company is duly incorporated and validly existing under
        the laws of the State of Wisconsin.

   2.   The Shares will, when certificates representing the Shares
        shall have been duly executed, countersigned and registered
        and delivered against receipt by the Company of the
        consideration therefor as set forth in resolutions of the
        Board of Directors of the Company adopted June 24, 1999, be
        legally issued, fully paid and nonassessable, except to the
        extent that such Shares are assessable as provided in
        Section 180.0622 of the Wisconsin Business Corporation Law
        and judicial interpretations thereof.

   We hereby consent to the filing of this opinion as an Exhibit to
the Registration Statement and to all references to our firm included
in or made a part of the Registration Statement.

                            Very truly yours,



                            Michael Best & Friedrich LLP