Registration No. 0-27854

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                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C.  20549

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                                AMENDMENT NO. 4
                                      TO
                                   FORM 10/A

                  GENERAL FORM FOR REGISTRATION OF SECURITIES
                      PURSUANT TO SECTION 12(b) OR (g) OF
                      THE SECURITIES EXCHANGE ACT OF 1934

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                         BONE CARE INTERNATIONAL, INC.
            (Exact name of registrant as specified in its charter)


          Wisconsin                                              39-1527471
(State or other jurisdiction of                               (I.R.S. employer
incorporation or organization)                               identification no.)

        One Science Court
        Madison, Wisconsin                                           53711
(Address of principal executive offices)                          (Zip code)


      Registrant's telephone number including area code:  (608) 274-2663

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       Securities to be registered pursuant to Section 12(b) of the Act:

                                     None

       Securities to be registered pursuant to Section 12(g) of the Act:

                          Common Stock, no par value
                        Preferred Stock Purchase Rights
                       (Title of class to be registered)

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ITEM 11.  Description of Registrant's Securities to be Registered.

     This amendment to Bone Care's Registration Statement on Form 10 is being
filed for the purpose of amending the description of the Shareholders Rights
Plan as amended by the First Amendment thereto which is filed as an Exhibit
hereto. The following amends and restates the "Description of Bone Care Capital
Stock" included in Bone Care's Registration Statement on Form 10.

                         DESCRIPTION OF CAPITAL STOCK

     We are authorized to issue up to 28,000,000 shares of common stock, no par
value, and 2,000,000 shares of preferred stock, par value $.001 per share. Our
board of directors has designated 140,000 shares of the preferred stock as
Series A Junior Participating Preferred Stock in connection with the rights
described below.

Common stock

     Holders of common stock are entitled to one vote for each share held on all
matters submitted to our shareholders. All outstanding shares of common stock
are validly issued, fully paid and nonassessable, except for certain statutory
liabilities which may be imposed by Wisconsin law for unpaid employee wages.
Wisconsin law provides that shareholders are personally liable to an amount
equal to the par value of the shares owned by them, if the shares have a par
value, and up to the price for which the shares without par value were issued,
for all debts owing to employees for services performed for the corporation.
Shareholders are not liable for wages to employees in excess of six months'
service for any individual employee. The common stock has no par value. Holders
of common stock are entitled to any dividends as our board of directors may
declare, so long as our funds are legally sufficient.

     If we liquidate, dissolve or wind-up our business, our assets will be
distributed ratably to shareholders after satisfying our obligations to
creditors.

     Holders of common stock do not have cumulative voting rights in the
election of directors and do not have any preemptive, subscription or redemption
rights.

Preferred stock

     Our board of directors is authorized, subject to limitations prescribed by
law or the rules of the Nasdaq Stock Market, to issue, without shareholder
approval, up to 2,000,000 shares of preferred stock and to determine the
preferences, limitations and relative rights of the preferred stock or any
series of preferred stock. In connection with the adoption of our shareholders
rights plan, our board of directors designated 140,000 shares as the Series A
Junior Participating Preferred Stock. See "--Rights Agreement."


                                      -1-



Rights agreement

     Our board of directors has adopted a shareholders rights plan. Under the
shareholders rights plan, as amended, each share of common stock has associated
with it one preferred share purchase right. The terms of the rights are set
forth in a rights agreement between us and Norwest Bank Minnesota, N.A. The plan
may have an anti-takeover effect by discouraging any person or group from
acquiring in excess of 20% of our common stock.

     Under certain circumstances described below, each right would entitle its
holder to purchase one two-hundredth of a share of Series A Junior Participating
Preferred Stock for a price of $50.00 per one two-hundredth of a share, subject
to adjustment. The rights are not presently exercisable and are transferable
only with the related shares of common stock. The rights will not become
exercisable or be evidenced by separate certificates or trade separately from
the common stock prior to the occurrence of certain triggering events described
below. In such an event, separate rights certificates would be issued and
distributed representing one right for each share of common stock. There is no
present market for the rights separate from the common stock and we cannot
predict whether a trading market would develop with respect to the rights if the
rights ever become exercisable.

     The rights would become exercisable at the specified exercise price upon
the earlier to occur of:

     .  10 business days after the first public announcement that any person or
        group (other than Bone Care, Dr. Mazess and their respective affiliates)
        has acquired beneficial ownership of 20% or more of our outstanding
        common stock; and

     .  10 business days (unless delayed by our board of directors) after any
        person or group (other than Bone Care, Dr. Mazess and their respective
        affiliates) has commenced, or announced the intention to commence, a
        tender or exchange offer which would, upon its consummation, result in
        such person or group being the beneficial owner of 20% or more of our
        common stock.

Rights certificates will be distributed as soon as practicable after the rights
become exercisable. Rights may not be exercised, however, following the
occurrence of an event described below under the caption "Flip-In" prior to the
expiration of our right to redeem the rights.

     Flip-In
     -------

     After the rights become exercisable, the holders of the rights (other than
the person who has triggered the exercisability of the rights and certain
transferees of such person whose rights are voided) would be entitled to
purchase common stock at a 50% discount.


                                      -2-


     Flip-Over
     ---------

     In the event that, on or after the date the rights become exercisable:

     .  we merge into or consolidate with the person who has triggered the
        exercisability of the rights, or its affiliates, or, unless all holders
        of the outstanding shares of common stock are treated the same, we merge
        into or consolidate with any other person,

     .  the person who has triggered the exercisability of the rights or its
        affiliates merges into us or, unless all holders of the outstanding
        shares of common stock are treated the same, any other person merges
        into us, or

     .  we sell or transfer 50% or more of our consolidated assets or earning
        power to the person who has triggered the exercisability of the rights
        or its affiliates or, unless all holders of the outstanding shares of
        common stock are treated the same, we sell or transfer 50% or more of
        our consolidated assets or earning power to any other person (with
        limited designated exceptions),

the holders of the rights (other than rights which have become void) would be
entitled to purchase our common stock or the common stock of the person which
acquires our business or assets at a 50% discount.

     Redemption of rights

     We may redeem the rights, in whole but not in part,
at a redemption price of $.005 per right, subject to adjustment, at the
direction of the board of directors, at any time prior to the earliest of:

     .  10 business days after the first public announcement that any person or
        group has triggered exercisability of the rights,

     .  the occurrence of any transaction described under the caption "Flip-
        Over," or

     .  April 13, 2006.

     Exchange of shares for rights

     At any time after any person or group has triggered exercisability of the
rights and before any person (other than Bone Care, Dr. Mazess and their
respective affiliates), together with its affiliates and associates, has become
the beneficial owner of 50% or more of the outstanding shares of common stock,
our board of directors may, at its option, exchange all or any part of the
rights (other than rights which have become void) for shares of common stock at
the exchange rate of one share of common stock (or one two-hundredth of a
preferred share) per right, subject to adjustment.

Terms of Series A Junior Participating Preferred Stock

     The Series A Junior Participating Preferred Stock which would be issuable
upon exercise of the rights (should the rights become exercisable) would not be
redeemable and would have the following terms which were designated by our board
of directors:

                                      -3-


     .  Each holder of a preferred share would be entitled to receive a
        preferential quarterly dividend equal to 200 times the aggregate per
        share amount of all cash dividends, plus 200 times the aggregate per
        share amount (payable in kind) of all non-cash dividends and other
        distributions (other than in shares of common stock), declared on the
        common stock during the quarter, adjusted to give effect to any dilution
        event, such as a dividend on the common stock payable in shares of
        common stock or any subdivision, combination or reclassification of the
        common stock.

     .  Each holder of a preferred share would be entitled to 200 votes on all
        matters submitted to a vote of our shareholders, voting together as a
        single class with the holders of our common stock and the holders of any
        other class of our capital stock having general voting rights, adjusted
        to give effect to any dilution event.

     .  In the event we liquidate, each holder of a preferred share would be
        entitled to receive a preferential liquidation payment equal to 200
        times the aggregate per share amount to be distributed to the holders of
        our common stock, adjusted to give effect to any dilution event, plus an
        amount equal to accrued and unpaid dividends and distributions on such
        preferred share, whether or not declared, to the date of such payment.

     .  In the event of any merger, consolidation or other transaction in which
        the outstanding shares of common stock are exchanged for or converted
        into other capital stock, securities, cash and/or other property, each
        preferred share would be similarly exchanged or converted into 200 times
        the per share amount applicable to the common stock, adjusted to give
        effect to any dilution event.

Articles of incorporation and by-laws

     Our articles of incorporation and by-laws contain terms which could have
the effect of delaying, deferring or preventing a takeover attempt that you
might consider to be in your best interest. These provisions are intended to
enhance the likelihood of continuity and stability in the composition of and in
the policies formulated by our board of directors. In addition, these provisions
are also intended to ensure that our board of directors will have sufficient
time to act in what it believes to be in our best interests and the best
interests of our shareholders.

     Classified board of directors

Our board of directors is divided into three classes of directors serving
staggered three-year terms. The classification of directors has the effect of
making it more difficult for shareholders to change the composition of our board
of directors in a short period of time. At least two annual meetings of
shareholders, instead of one, will generally be required to effect a change in a
majority of our board of directors.

                                      -4-


     Number of directors; filling vacancies; removal

     Our board of directors is designed to consist of at least five and no more
than twelve members as fixed by the by-laws. The by-laws currently fix the
number of directors at five. The by-laws provide that our board of directors,
acting by majority vote of the directors then in office, may fill any newly
created directorships or vacancies on our board of directors. The articles of
incorporation and the by-laws provide that a director may be removed upon the
affirmative vote of 80% of the outstanding shares entitled to vote for the
election of such directors, and any vacancy so created may be filled by the
affirmative vote of 80% of such shares.

     Super-majority vote

     In voting on a merger or consolidation by us with or into any other
corporation, or sale, lease or exchange of all or substantially all of our
property and assets, our articles of incorporation require the approval by an
affirmative vote of 60% of the shares of common stock then entitled to vote.

     Shareholder advance notice requirements

     Our by-laws provide that for nominations for our board of directors or for
other business to be properly brought by a shareholder before an annual or
special meeting of shareholders, the shareholder must first have given notice
thereof in writing to our Secretary. To be timely, a shareholder's notice
generally must be delivered not more than 90 days nor less than 60 days prior to
the date of the meeting. In addition, the notice must contain, among other
things, certain information about the shareholder delivering the notice and, as
applicable, background information about each nominee or a description of the
proposed business to be brought before the meeting.

     Preferred stock

     Although our board of directors has no intention at the present time of
doing so, we could issue a series of preferred stock that could, depending on
the terms of such series, impede the completion of a merger, tender offer or
other takeover attempt. Our board of directors will make any determination to
issue such shares based on its judgment as to our best interests and the best
interests of our shareholders. Our board of directors, in so acting, could issue
preferred stock having terms that could discourage an acquisition attempt
through which an acquiror may be able to change the composition of our board of
directors, including a tender offer or other transaction that some, or a
majority, of our shareholders might believe to be in their best interests or in
which shareholders might receive a premium over the then-current market price of
our common stock.

Certain effects of the rights plan

     The rights plan is designed to protect our shareholders in the event of
unsolicited offers to acquire all of our common stock and other coercive
takeover tactics which, in the opinion of our board of directors, could impair
its ability to represent shareholder interests. The provisions of the

                                      -5-


rights agreement may render an unsolicited takeover more difficult or less
likely to occur or might prevent such a takeover, even though such takeover may
offer our shareholders the opportunity to sell their stock at a price above the
then prevailing market rate and may be favored by a majority of our
shareholders. See "--Rights Agreement."

Certain Wisconsin Business Corporation Law provisions

     We are incorporated under the laws of the state of Wisconsin and conduct
business from our corporate headquarters in Madison, Wisconsin. Accordingly, we
are subject to several provisions of Wisconsin law which could have an anti-
takeover effect.

     Restrictions on business combinations

     Wisconsin law provides that a resident domestic corporation, may not engage
in a business combination with a person beneficially owning 10% of the voting
power of the outstanding voting stock for three years after the date the person
acquired its 10% or greater interest, unless the business combination, or the
acquisition of 10% or greater interest, received prior approval by the
corporation's board of directors. After the three-year period, a business
combination that was not so approved by the corporation's board of directors can
be consummated only if it is approved by the affirmative vote of a majority of
the outstanding voting shares not beneficially owned by the 10% shareholder or
is made at a specified formula price intended to provide a fair price for the
shares held by noninterested shareholders.

     In addition, Wisconsin law provides that business combinations involving a
person who beneficially owns, directly or indirectly, 10% or more of the voting
stock of the corporation, or an affiliate of the corporation which beneficially
owned, directly or indirectly, 10% or more of the voting stock of the
corporation within the last two years and a Wisconsin corporation with total
assets exceeding $1,000,000, a class of equity securities held of record by 500
or more persons, and with at least 100 shareholders of record with unlimited
voting rights who are Wisconsin residents are subject to a supermajority vote of
shareholders, in addition to any approval otherwise required. Under Wisconsin
law, a business combination described above must be approved by 80% of the
voting power of the corporation's stock and at least two-thirds of the voting
power of the corporation's stock not beneficially held by the 10% shareholder
who is party to the transaction or any of its affiliates or associates, in each
case voting together as a single group, unless the following fair price
standards have been met:

     .  the aggregate value of the per share consideration is equal to the
        higher of:

        .  the highest price paid for any common stock of the corporation by the
           10% shareholder in the transaction in which it became a 10%
           shareholder or within two years before the date of the business
           combination,

        .  the market value of the corporation's shares on the date of
           commencement of any tender offer by the 10% shareholder, the date on
           which the person

                                      -6-


           became a 10% shareholder or the date of the first public announcement
           of the proposed business combination, whichever is highest, or

        .  the highest liquidation or dissolution distribution to which holders
           of shares would be entitled, and

     .  either cash, or the form of consideration used by the 10% shareholder to
        acquire the largest number of shares, is offered.

Our articles of incorporation provide that neither Dr. Mazess, any affiliate of
Dr. Mazess nor the estate, executor, administrator, conservator or beneficiaries
of Dr. Mazess shall be subject to the fair price restrictions described above.

     Stock purchase restrictions

     Wisconsin law provides that, in addition to the vote otherwise required by
law or the articles of incorporation of a Wisconsin corporation with total
assets exceeding $1,000,000, a class of equity securities held of record by 500
or more persons, and with at least 100 shareholders of record with unlimited
voting rights who are Wisconsin residents, the approval of the holders of a
majority of the shares entitled to vote is required before such corporation can
take certain action while a takeover offer is being made or after a takeover
offer has been publicly announced and before it is concluded. Shareholder
approval is required for the corporation to:

     .  acquire more than 5% of its outstanding voting shares at a price above
        the market price from any individual or organization that owns more than
        3% of the outstanding voting shares and has held such shares for less
        than two years, unless a similar offer is made to acquire all voting
        shares, or

     .  sell or option assets of the corporation which amount to at least 10% of
        the market value of the corporation unless at least a majority of at
        least three independent directors vote not to have this provision apply
        to the corporation.

The restrictions described above may have the effect of deterring a shareholder
from acquiring our shares with the goal of seeking to have us repurchase such
shares at a premium over the market price or, alternatively, may deter a person
from embarking on an acquisition in which shareholders might receive a premium
for their stock over the then-current market price.

     Control share voting restrictions

     Wisconsin law provides that, absent a contrary provision in the articles of
incorporation, the voting power of shares (including shares issuable upon
conversion of convertible securities or upon exercise of options or warrants) of
a Wisconsin corporation with total assets exceeding $1,000,000, a class of
equity securities held of record by 500 or more persons, and with at least 100
shareholders of record with unlimited voting rights who are Wisconsin residents
held by any person in excess of 20% of the voting power in the election of
directors is limited to 10% of the

                                      -7-


full voting power of such excess shares unless, at a special meeting of
shareholders, the affirmative vote of a majority of the voting power represented
at the meeting and entitled to vote on the subject matter approve a resolution
restoring full voting power to such shares. Shares of the corporation held or
acquired from the corporation or acquired under an agreement entered into at a
time when the corporation did not qualify for the specified treatment are
excluded from the application of these provisions. The articles of incorporation
provide that this provision of Wisconsin law should not in any way limit the
voting power of any shares of capital stock owned by Dr. Mazess, any affiliate
of Dr. Mazess or the estate, administrator, conservator or beneficiaries of Dr.
Mazess.

Transfer agent and registrar

     The Transfer Agent and Registrar for the common stock is Norwest Bank
Minnesota, N.A.

Item 15.  Financial Statements and Exhibits

         The following amends and restates the Exhibit Index which was included
in Bone Care's Registration Statement on Form 10 for purposes of Item 15(b).

     (b)  Exhibits


Exhibit Number
- --------------
   3.1(a)     Restated Articles of Incorporation of Bone Care*
   3.1(b)     Articles of Amendment of Bone Care (incorporated by reference to
                exhibit 3.1(b) of Bone Care's Form S-1 Registration Statement
                (Registration No. 333-43923) (the "Form S-1"))
   3.2        By-Laws of Bone Care (incorporated by reference to exhibit 3.2 of
                Bone Care's Quarterly Report on Form 10-Q for the quarter ended
                December 31, 1996 (File No. 0-27854))
   4.1        Shareholders Rights Agreement between Bone
                Care and Norwest Bank Minnesota, N.A.*
   4.2        First Amendment to Shareholders Rights Agreement
                between Bone Care and Norwest Bank Minnesota, N.A.
   5.1        Opinion of KPMG (formerly KPMG Peat Marwick LLP) LLP*
  10.1        Distribution Agreement between Lunar and Bone Care*
  10.2        Tax Disaffiliation Agreement between Lunar and Bone Care*
  10.3        Transition Agreement between Lunar and Bone Care*
  10.4        Incentive Stock Option Plan of Bone Care*
  10.5        Bone Care International, Inc. 1996 Stock Option Plan (incorporated
                by reference to exhibit 10.5 of the Form S-1).
  10.6        Amended and Restated License Agreement effective as of June 8,
                1998 between Bone Care and Draxis Health Inc. (incorporated by
                reference to exhibit 10.6 of the Form S-1).
  10.7        Form of Stock Option Agreement (incorporated by reference to
                exhibit 10.7 of the Form S-1).
  10.8        Agreement, effective as of May 1, 1987, between the Wisconsin
                Alumni Research Foundation and Bone Care (confidential
                information appearing in this document has been omitted and
                filed separately with the Securities and Exchange Commission in
                accordance with the Securities Act of 1933, as amended, and 17
                C.F.R. 230.406 and 200.80 promulgated thereunder. Omitted
                information has been replaced with asterisks) (incorporated by
                reference to exhibit 10.8 of the Form S-1).

- ------------------------------
*    Previously filed.

                                      -8-


                                  SIGNATURES

     Pursuant to the requirements of Section 12 of the Securities and Exchange
Act of 1934, the registrant has duly caused this registration statement to be
signed on its behalf by the undersigned, thereunto duly authorized.


                                           BONE CARE INTERNATIONAL, INC.



September 22, 1999                         By /s/ Dale W. Gutman
                                              ----------------------------------
                                              Name:  Dale W. Gutman
                                              Title:  Vice President - Finance

                                      -9-


                                 EXHIBIT INDEX
                                      TO
                           REGISTRATION STATEMENT ON
                                    FORM 10
                       FOR BONE CARE INTERNATIONAL, INC.



Exhibit Number
- --------------
           
   3.1(a)     Restated Articles of Incorporation of Bone Care*
   3.1(b)     Articles of Amendment of Bone Care (incorporated by reference to
                exhibit 3.1(b) of Bone Care's Form S-1 Registration Statement
                (Registration No. 333-43923) (the "Form S-1"))
   3.2        By-Laws of Bone Care (incorporated by reference to exhibit 3.2 of
                Bone Care's Quarterly Report on Form 10-Q for the quarter ended
                December 31, 1996 (File No. 0-27854))
   4.1        Shareholders Rights Agreement between Bone
                Care and Norwest Bank Minnesota, N.A.*
   4.2        First Amendment to Shareholders Rights Agreement
                between Bone Care and Norwest Bank Minnesota, N.A.
   5.1        Opinion of KPMG (formerly KPMG Peat Marwick LLP) LLP*
  10.1        Distribution Agreement between Lunar and Bone Care*
  10.2        Tax Disaffiliation Agreement between Lunar and Bone Care*
  10.3        Transition Agreement between Lunar and Bone Care*
  10.4        Incentive Stock Option Plan of Bone Care*
  10.5        Bone Care International, Inc. 1996 Stock Option Plan (incorporated
                by reference to exhibit 10.5 of the Form S-1).
  10.6        Amended and Restated License Agreement effective as of June 8,
                1998 between Bone Care and Draxis Health Inc. (incorporated by
                reference to exhibit 10.6 of the Form S-1).
  10.7        Form of Stock Option Agreement (incorporated by reference to
                exhibit 10.7 of the Form S-1).
  10.8        Agreement, effective as of May 1, 1987, between the Wisconsin
                Alumni Research Foundation and Bone Care (confidential
                information appearing in this document has been omitted and
                filed separately with the Securities and Exchange Commission in
                accordance with the Securities Act of 1933, as amended, and 17
                C.F.R. 230.406 and 200.80 promulgated thereunder. Omitted
                information has been replaced with asterisks) (incorporated by
                reference to exhibit 10.8 of the Form S-1).


- ------------------------------
*    Previously filed.