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                                                                    EXHIBIT 10.4

                    AMERICAN PHARMACEUTICAL PARTNERS, INC.

                       2001 EMPLOYEE STOCK PURCHASE PLAN
                       ---------------------------------

          The following constitute the provisions of the 2001 Employee Stock
Purchase Plan of American Pharmaceutical Partners, Inc.

          1.   Purpose.  The purpose of the Plan is to provide employees of the
               -------
Company and its Designated Parents or Subsidiaries with an opportunity to
purchase Common Stock of the Company through accumulated payroll deductions.  It
is the intention of the Company to have the Plan qualify as an "Employee Stock
Purchase Plan" under Section 423 of the Code.  The provisions of the Plan,
accordingly, shall be construed so as to extend and limit participation in a
manner consistent with the requirements of that section of the Code.

          2.   Definitions.  As used herein, the following definitions shall
               -----------
apply:

          (a)  "Administrator" means either the Board or a committee of the
                -------------
Board that is responsible for the administration of the Plan as is designated
from time to time by resolution of the Board.

          (b)  "Applicable Laws" means the legal requirements relating to the
                ---------------
administration of employee stock purchase plans, if any, under applicable
provisions of federal securities laws, state corporate and securities laws, the
Code, the rules of any applicable stock exchange or national market system, and
the rules of any foreign jurisdiction applicable to participation in the Plan by
residents therein.

          (c)  "Board" means the Board of Directors of the Company.
                -----

          (d)  "Change in Control" means a change in ownership or control of the
                -----------------
Company effected through the direct or indirect acquisition by any person or
related group of persons (other than an acquisition from or by the Company or by
a Company-sponsored employee benefit plan or by a person that directly or
indirectly controls, is controlled by, or is under common control with, the
Company) of beneficial ownership (within the meaning of Rule 13d-3 of the
Exchange Act) of securities possessing more than fifty percent (50%) of the
total combined voting power of the Company's outstanding securities.

          (e)  "Code" means the Internal Revenue Code of 1986, as amended.
                ----

          (f)  "Common Stock" means the common stock of the Company.
                ------------

          (g)  "Company" means American Pharmaceutical Partners, Inc., a
                -------
Delaware corporation.

          (h)  "Compensation" means an Employee's base salary from the Company
                ------------
or one or more Designated Parents or Subsidiaries, including such amounts of
base salary as are deferred by the Employee (i) under a qualified cash or
deferred arrangement described in Section

                                       1
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401(k) of the Code, or (ii) to a plan qualified under Section 125 of the Code.
Compensation does not include overtime, bonuses, annual awards, other incentive
payments, reimbursements or other expense allowances, fringe benefits (cash or
noncash), moving expenses, deferred compensation, contributions (other than
contributions described in the first sentence) made on the Employee's behalf by
the Company or one or more Designated Parents or Subsidiaries under any employee
benefit or welfare plan now or hereafter established, and any other payments not
specifically referenced in the first sentence.

          (i)  "Corporate Transaction" means any of the following transactions:
                ---------------------

               (1) a merger or consolidation in which the Company is not the
          surviving entity, except for a transaction the principal purpose of
          which is to change the state in which the Company is incorporated;

               (2) the sale, transfer or other disposition of all or
          substantially all of the assets of the Company (including the capital
          stock of the Company's subsidiary corporations);

               (3) the complete liquidation or dissolution of the Company;

               (4) any reverse merger in which the Company is the surviving
          entity but in which securities possessing more than fifty percent
          (50%) of the total combined voting power of the Company's outstanding
          securities are transferred to a person or persons different from those
          who held such securities immediately prior to such merger; or

               (5) acquisition in a single or series of related transactions by
          any person or related group of persons (other than the Company or by a
          Company-sponsored employee benefit plan) of beneficial ownership
          (within the meaning of Rule 13d-3 of the Exchange Act) of securities
          possessing more than fifty percent (50%) of the total combined voting
          power of the Company's outstanding securities but excluding any such
          transaction or series of related transactions that the Administrator
          determines shall not be a Corporate Transaction.

          (j)  "Designated Parents or Subsidiaries" means the Parents or
                ----------------------------------
Subsidiaries which have been designated by the Administrator from time to time
as eligible to participate in the Plan.

          (k)  "Effective Date" means the effective date of the Registration
                --------------
Statement relating to the Company's initial public offering of its Common Stock.
However, should any Designated Parent or Subsidiary become a participating
company in the Plan after such date, then such entity shall designate a separate
Effective Date with respect to its employee-participants.

          (l)  "Employee" means any individual, including an officer or
                --------
director, who is an employee of the Company or a Designated Parent or Subsidiary
for purposes of Section 423 of the Code. For purposes of the Plan, the
employment relationship shall be treated as continuing intact while the
individual is on sick leave or other leave of absence approved by the
individual's

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employer. Where the period of leave exceeds ninety (90) days and the
individual's right to reemployment is not guaranteed either by statute or by
contract, the employment relationship will be deemed to have terminated on the
ninety-first (91st) day of such leave, for purposes of determining eligibility
to participate in the Plan.

          (m)  "Enrollment Date" means the first day of each Offer Period.
                ---------------

          (n)  "Exchange Act" means the Securities Exchange Act of 1934, as
                ------------
amended.

          (o)  "Exercise Date" means the last day of each Purchase Period.
                -------------

          (p)  "Fair Market Value" means, as of any date, the value of Common
                -----------------
Stock determined as follows:

               (1) If the Common Stock is listed on any established stock
          exchange or a national market system, including without limitation The
          Nasdaq National Market or The Nasdaq SmallCap Market of The Nasdaq
          Stock Market, its Fair Market Value shall be the closing sales price
          for such stock (or the closing bid, if no sales were reported) as
          quoted on such exchange or system on the date of determination (or, if
          no closing sales price or closing bid was reported on that date, as
          applicable, on the last trading date such closing sales price or
          closing bid was reported), as reported in The Wall Street Journal or
          such other source as the Administrator deems reliable;

               (2) If the Common Stock is regularly quoted on an automated
          quotation system (including the OTC Bulletin Board) or by a recognized
          securities dealer, but selling prices are not reported, the Fair
          Market Value of a Share of Common Stock shall be the mean between the
          high bid and low asked prices for the Common Stock on date of
          determination (or, if no such prices were reported on that date, on
          the last date such prices were reported), as reported in The Wall
          Street Journal or such other source as the Administrator deems
          reliable;

               (3) In the absence of an established market for the Common Stock
          of the type described in (1) and (2), above, the Fair Market Value
          thereof shall be determined by the Administrator in good faith and in
          a manner consistent with Section 260.140.50 of Title 10 of the
          California Code of Regulations which requires that consideration be
          given to (A) the price at which securities of reasonably comparable
          corporations (if any) in the same industry are being traded, or (B) if
          there are no securities of reasonably comparable corporations in the
          same industry being traded, the earnings history, book value and
          prospects of the issuer in light of market conditions generally; or

               (4) On the initial Effective Date of the Plan, the Fair Market
          Value shall be the price at which the Board, or if applicable, the
          Pricing Committee of the Board, and the underwriters agree to offer
          the Common Stock to the public in the initial public offering of the
          Common Stock.

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          (q)  "Offer Period" means an Offer Period established pursuant to
                ------------
Section 4 hereof.

          (r)  "Parent" means a "parent corporation," whether now or hereafter
                ------
existing, as defined in Section 424(e) of the Code.

          (s)  "Participant" means an Employee of the Company or Designated
                -----------
Parent or Subsidiary who is actively participating in the Plan.

          (t)  "Plan" means this Employee Stock Purchase Plan.
                ----

          (u)  "Purchase Period" means a period of approximately six months,
                ---------------
commencing on February 1 and August 1 of each year and terminating on the next
following July 31 or January 31, respectively; provided, however, that the first
Purchase Period shall commence on the Effective Date and shall end on July 31,
2002.

          (v)  "Purchase Price" shall  mean an amount equal to 85% of the Fair
                --------------
Market Value of a share of Common Stock on the Enrollment Date or on the
Exercise Date, whichever is lower.

          (w)  "Reserves" means the sum of the number of shares of Common Stock
                --------
covered by each option under the Plan which have not yet been exercised and the
number of shares of Common Stock which have been authorized for issuance under
the Plan but not yet placed under option.

          (x)  "Subsidiary" means a "subsidiary corporation," whether now or
                ----------
hereafter existing, as defined in Section 424(f) of the Code.

          3.   Eligibility.
               -----------

          (a)  General.  Any individual who is an Employee on a given Enrollment
               -------
Date shall be eligible to participate in the Plan for the Offer Period
commencing with such Enrollment Date.

          (b)  Limitations on Grant and Accrual.  Any provisions of the Plan to
               --------------------------------
the contrary notwithstanding, no Employee shall be granted an option under the
Plan (i) if, immediately after the grant, such Employee (taking into account
stock owned by any other person whose stock would be attributed to such Employee
pursuant to Section 424(d) of the Code) would own stock and/or hold outstanding
options to purchase stock possessing five percent (5%) or more of the total
combined voting power or value of all classes of stock of the Company or of any
Parent or Subsidiary, or (ii) which permits the Employee's rights to purchase
stock under all employee stock purchase plans of the Company and its Parents or
Subsidiaries to accrue at a rate which exceeds Twenty-Five Thousand Dollars
($25,000) worth of stock (determined at the Fair Market Value of the shares at
the time such option is granted) for each calendar year in which such option is
outstanding at any time.  The determination of the accrual of the right to
purchase stock shall be made in accordance with Section 423(b)(8) of the Code
and the regulations thereunder.

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          (c)  Other Limits on Eligibility.  Notwithstanding Subsection (a),
               ---------------------------
above, the following Employees shall not be eligible to participate in the Plan
for any relevant Offer Period: (i) Employees whose customary employment is 20
hours or less per week; (ii) Employees whose customary employment is for not
more than 5 months in any calendar year; (iii) Employees who have been employed
for fewer than three business days; and (iv) Employees who are subject to rules
or laws of a foreign jurisdiction that prohibit or make impractical the
participation of such Employees in the Plan.

          4.   Offer Periods.
               -------------

          (a)  The Plan shall be implemented through overlapping or consecutive
Offer Periods until such time as (i) the maximum number of shares of Common
Stock available for issuance under the Plan shall have been purchased or (ii)
the Plan shall have been sooner terminated in accordance with Section 19 hereof.
The maximum duration of an Offer Period shall be twenty-seven (27) months.
Initially, the Plan shall be implemented through overlapping Offer Periods of
twenty-four (24) months' duration commencing each February 1 and August 1
following the Effective Date (except that the initial Offer Period shall
commence on the Effective Date and shall end on January 31, 2004).

          (b)  A Participant shall be granted a separate option for each Offer
Period in which he or she participates.  The option shall be granted on the
Enrollment Date and shall be automatically exercised in successive installments
on the Exercise Dates ending within the Offer Period.

          (c)  If on the first day of any Purchase Period in an Offer Period in
which a Participant is participating, the Fair Market Value of the Common Stock
is less than the Fair Market Value of the Common Stock on the Enrollment Date of
the Offer Period (after taking into account any adjustment during the Offer
Period pursuant to Section 18(a)), the Offer Period shall be terminated
automatically and the Participant shall be enrolled automatically in the new
Offer Period which has its first Purchase Period commencing on that date,
provided the Participant is eligible to participate in the Plan on that date and
has not elected to terminate participation in the Plan.

          (d)  Except as specifically provided herein, the acquisition of Common
Stock through participation in the Plan for any Offer Period shall neither limit
nor require the acquisition of Common Stock by a Participant in any subsequent
Offer Period.

          5.   Participation.
               -------------

          (a)  All Employees eligible to participate in the Plan as of the first
Enrollment Date of the Plan shall automatically become a Participant in the
initial Offer Period and be eligible to make a direct payment for shares of the
Common Stock on the Exercise Date of the first Purchase Period of the initial
Offer Period in an amount equal to the lesser of the aggregate Purchase Price
for six hundred twenty-five (625) shares of the Common Stock or ten percent
(10%) of the Compensation that he or she receives during the first Purchase
Period of the initial Offer Period, unless a change of status notice in the form
of Exhibit C to this Plan (or such other

                                       5
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form (including electronic forms) as determined by the Administrator from time
to time) is filed to the contrary or the Participant withdraws from the Plan as
provided in Section 10. No subscription agreement need be filed by the
Participant with the Company in order to participate in the initial Offer
Period.

          (b)  After the initial Offer Period, an eligible Employee may become a
Participant in the Plan by completing a subscription agreement authorizing
payroll deductions in the form of Exhibit A to this Plan (or such other form
(including electronic forms) as determined by the Administrator from time to
time) and filing it with the designated payroll office of the Company at least
three (3) business days prior to the Enrollment Date for the Offer Period in
which such participation will commence, unless a later time for filing the
subscription agreement is set by the Administrator for all eligible Employees
with respect to a given Offer Period.

          (c)  No payroll deductions shall be made for Participants during the
first Purchase Period of the initial Offer Period, unless a change of status
notice in the form of Exhibit C to this Plan (or such other form (including
electronic forms) as determined by the Administrator from time to time)
authorizing the commencement of payroll deductions is filed by the Participant
with the Company after a registration statement on Form S-8 has been filed with
the Securities Exchange Commission with respect to the shares being offered
under the Plan.  If so elected, the rate of payroll deductions during the first
Purchase Period of the initial Offer Period may exceed the maximum permitted
rate under Section 6(a) to make-up for missed payroll deductions that would
otherwise have been made prior to the filing of the Form S-8 with respect to the
Plan.  Payroll deductions for a Participant in the initial Offer Period shall
commence at the rate elected by the Participant under Section 6(a) with the
first partial or full payroll period beginning on the first day of the second
Purchase Period of the initial Offer Period and shall end on the last complete
payroll period during the initial Offer Period, unless a change of status notice
in the form of Exhibit B (or such other form (including electronic forms) as
determined by the Administrator from time to time) is filed to the contrary or
the Participant withdraws from the Plan as provided in Section 10.  No direct
payment for shares shall be permitted after the first Purchase Period of the
initial Offer Period.  Therefore, Participants in the initial Offer Period must
file the change of status notice in the form of Exhibit C to this Plan (or such
other form (including electronic forms) as determined by the Administrator from
time to time) prior to the commencement of the second Purchase Period of the
initial Offer Period to assure maximum participation rights under the Plan.

          (d)  For Offer Periods, other than the initial Offer Period, payroll
deductions for a Participant shall commence with the first partial or full
payroll period beginning on the Enrollment Date and shall end on the last
complete payroll period during the Offer Period, unless sooner terminated by the
Participant as provided in Section 10.

          6.   Payroll Deductions.
               ------------------

          (a)  At the time a Participant files a subscription agreement, the
Participant shall elect to have payroll deductions made during the Offer Period
in amounts between one percent (1%) and not exceeding ten percent (10%) of the
Compensation which the Participant receives during the Offer Period.

                                       6
<PAGE>

          (b)  All payroll deductions made for a Participant shall be credited
to the Participant's account under the Plan and will be withheld in whole
percentages only. A Participant may not make any additional payments into such
account.

          (c)  A Participant may discontinue participation in the Plan as
provided in Section 10, or may increase or decrease the rate of payroll
deductions during the Offer Period by completing and filing with the Company a
change of status notice in the form of Exhibit B to this Plan (or such other
form (including electronic forms) as determined by the Administrator from time
to time) authorizing an increase or decrease in the payroll deduction rate.
During the first Purchase Period of the initial Offer Period, a Participant may
discontinue participation in the Plan as provided in Section 10 or initiate
payroll deductions by completing and filing with the Company a change of status
notice in the form of Exhibit C to this Plan (or such other form (including
electronic forms) as determined by the Administrator from time to time).  Any
increase or decrease in the rate of a Participant's payroll deductions shall be
effective with the first full payroll period commencing three (3) business days
after the Company's receipt of the change of status notice unless the Company
elects to process a given change in participation more quickly.  A Participant's
subscription agreement (as modified by any change of status notice) shall remain
in effect for successive Offer Periods unless terminated as provided in Section
10.  The Administrator shall be authorized to limit the number of payroll
deduction rate changes during any Offer Period.

          (d)  Notwithstanding the foregoing, to the extent necessary to comply
with Section 423(b)(8) of the Code and Section 3(b) herein, a Participant's
payroll deductions shall be decreased to 0%.  Payroll deductions shall
recommence at the rate provided in such Participant's subscription agreement, as
amended, at the time when permitted under Section 423(b)(8) of the Code and
Section 3(b) herein, unless such participation is sooner terminated by the
Participant as provided in Section 10.

          7.   Grant of Option.  On the Enrollment Date, each Participant shall
               ---------------
be granted an option to purchase (at the applicable Purchase Price) two thousand
five hundred (2,500) shares of the Common Stock, subject to adjustment as
provided in Section 18 hereof; provided (i) that such option shall be subject to
the limitations set forth in Sections 3(b), 6 and 12 hereof, and (ii) the
maximum number of shares of Common Stock a Participant shall be permitted to
purchase in any Purchase Period shall be six hundred twenty-five (625) shares,
subject to adjustment as provided in Section 18 hereof.  Exercise of the option
shall occur as provided in Section 8, unless the Participant has withdrawn
pursuant to Section 10, and the option, to the extent not exercised, shall
expire on the last day of the Offer Period.

          8.   Exercise of Option.  Unless a Participant withdraws from the Plan
               ------------------
as provided in Section 10, below, the Participant's option for the purchase of
shares will be exercised automatically on each Exercise Date, by applying the
accumulated payroll deductions in the Participant's account to purchase the
number of full shares subject to the option by dividing such Participant's
payroll deductions accumulated prior to such Exercise Date and retained in the
Participant's account as of the Exercise Date by the applicable Purchase Price,
provided, however, that if a Participant is eligible to purchase any shares on
the first Exercise Date of the initial Offer Period by direct payment, the
Participant's option for the purchase of

                                       7
<PAGE>

shares will be exercised to the extent possible by applying the direct payment
amount made by the Participant to purchase the number of full shares subject to
the option by dividing such direct payment amount by the applicable Purchase
Price and, provided, further, in no event may the accumulated payroll deductions
and direct payment amounts applied to the purchase of shares on the first
Exercise Date of the initial Offer Period exceed the amount specified in Section
5(a). No fractional shares will be purchased; any payroll deductions accumulated
in a Participant's account which are not sufficient to purchase a full share
shall be carried over to the next Purchase Period or Offer Period, whichever
applies, or returned to the Participant, if the Participant withdraws from the
Plan. Any direct payment amounts which are not sufficient to purchase a full
share shall be returned to the Participant. Notwithstanding the foregoing, any
amount remaining in a Participant's account or any excess direct payment amount
following the purchase of shares on the Exercise Date due to the application of
Section 423(b)(8) of the Code or Section 7, above, shall be returned to the
Participant and shall not be carried over to the next Offer Period or Purchase
Period. During a Participant's lifetime, a Participant's option to purchase
shares hereunder is exercisable only by the Participant.

          9.   Delivery.  Upon receipt of a request from a Participant after
               --------
each Exercise Date on which a purchase of shares occurs, the Company shall
arrange the delivery to such Participant, as promptly as practicable, of a
certificate representing the shares purchased upon exercise of the Participant's
option.

          10.  Withdrawal; Termination of Employment.
               -------------------------------------

          (a)  A Participant may either (i) withdraw all but not less than all
the payroll deductions credited to the Participant's account and not yet used to
exercise the Participant's option under the Plan or (ii) terminate future
payroll deductions, but allow accumulated payroll deductions to be used to
exercise the Participant's option under the Plan at any time by giving written
notice to the Company in the form of Exhibit B to this Plan (or such other form
(including electronic forms) as determined by the Administrator from time to
time).  During the first Purchase Period of the initial Offer Period, a
Participant may elect to withdraw from the Plan and not purchase shares by
direct payment by giving written notice to the Company in the form of Exhibit C
to this Plan (or such other form (including electronic forms) as determined by
the Administrator from time to time).  If the Participant elects withdrawal
alternative (i) described above, all of the Participant's payroll deductions
credited to the Participant's account will be paid to such Participant as
promptly as practicable after receipt of notice of withdrawal, such
Participant's option for the Offer Period will be automatically terminated, and
no further payroll deductions for the purchase of shares will be made during the
Offer Period.  If the Participant elects withdrawal alternative (ii) described
above, no further payroll deductions for the purchase of shares will be made
during the Offer Period, all of the Participant's payroll deductions credited to
the Participant's account will be applied to the exercise of the Participant's
option on the next Exercise Date, and after such Exercise Date, such
Participant's option for the Offer Period will be automatically terminated.  If
a Participant withdraws from an Offer Period, payroll deductions will not resume
at the beginning of the succeeding Offer Period unless the Participant delivers
to the Company a new subscription agreement.

                                       8
<PAGE>

          (b)  Upon termination of a Participant's employment relationship (as
described in Section 2(k)) at a time more than three (3) months from the next
scheduled Exercise Date, the payroll deductions credited to such Participant's
account during the Offer Period but not yet used to exercise the option will be
returned to such Participant or, in the case of his/her death, to the person or
persons entitled thereto under Section 14, and such Participant's option will be
automatically terminated.  Upon termination of a Participant's employment
relationship (as described in Section 2(k)) within three (3) months of the next
scheduled Exercise Date, the payroll deductions credited to such Participant's
account during the Offer Period but not yet used to exercise the option will be
applied to the purchase of Common Stock on the next Exercise Date, unless the
Participant (or in the case of the Participant's death, the person or persons
entitled to the Participant's account balance under Section 14) withdraws from
the Plan by submitting a change of status notice in accordance with subsection
(a) of this Section 10.  In such a case, no further payroll deductions will be
credited to the Participant's account following the Participant's termination of
employment and the Participant's option under the Plan will be automatically
terminated after the purchase of Common Stock on the next scheduled Exercise
Date.

          11.  Interest.  No interest shall accrue on the payroll deductions
               --------
credited to a Participant's account under the Plan.

          12.  Stock.
               -----

          (a)  Subject to adjustment upon changes in capitalization of the
Company as provided in Section 18, the maximum number of shares of Common Stock
which shall be made available for sale under the Plan shall be two million
(2,000,000) shares, plus an annual increase to be added on the first day of the
Company's fiscal year beginning in 2002 equal to the lesser of (i) one million
five hundred thousand (1,500,000) shares, (ii) two percent (2%) of the
outstanding shares of Common Stock on such date, or (iii) a lesser number of
shares determined by the Administrator.  If the Administrator determines that on
a given Exercise Date the number of shares with respect to which options are to
be exercised may exceed (x) the number of shares then available for sale under
the Plan or (y) the number of shares available for sale under the Plan on the
Enrollment Date(s) of one or more of the Offer Periods in which such Exercise
Date is to occur, the Administrator may make a pro rata allocation of the shares
remaining available for purchase on such Enrollment Dates or Exercise Date, as
applicable, in as uniform a manner as shall be practicable and as it shall
determine to be equitable, and shall either continue all Offer Periods then in
effect or terminate any one or more Offer Periods then in effect pursuant to
Section 19, below.

          (b)  A Participant will have no interest or voting right in shares
covered by the Participant's option until such shares are actually purchased on
the Participant's behalf in accordance with the applicable provisions of the
Plan.  No adjustment shall be made for dividends, distributions or other rights
for which the record date is prior to the date of such purchase.

          (c)  Shares to be delivered to a Participant under the Plan will be
registered in the name of the Participant or in the name of the Participant and
his or her spouse.

                                       9
<PAGE>

          13.  Administration.  The Plan shall be administered by the
               --------------
Administrator which shall have full and exclusive discretionary authority to
construe, interpret and apply the terms of the Plan, to determine eligibility
and to adjudicate all disputed claims filed under the Plan.  Every finding,
decision and determination made by the Administrator shall, to the full extent
permitted by Applicable Law, be final and binding upon all persons.

          14.  Designation of Beneficiary.
               --------------------------

          (a)  Each Participant will file a written designation of a beneficiary
who is to receive any shares and cash, if any, from the Participant's account
under the Plan in the event of such Participant's death.  If a Participant is
married and the designated beneficiary is not the spouse, spousal consent shall
be required for such designation to be effective.

          (b)  Such designation of beneficiary may be changed by the Participant
(and the Participant's spouse, if any) at any time by written notice.  In the
event of the death of a Participant and in the absence of a beneficiary validly
designated under the Plan who is living (or in existence) at the time of such
Participant's death, the Company shall deliver such shares and/or cash to the
executor or administrator of the estate of the Participant, or if no such
executor or administrator has been appointed (to the knowledge of the
Administrator), the Administrator shall deliver such shares and/or cash to the
spouse (or domestic partner, as determined by the Administrator) of the
Participant, or if no spouse (or domestic partner) is known to the
Administrator, then to the issue of the Participant, such distribution to be
made per stirpes (by right of representation), or if no issue are known to the
Administrator, then to the heirs at law of the Participant determined in
accordance with Section 27.

          15.  Transferability.  Neither payroll deductions credited to a
               ---------------
Participant's account nor any rights with regard to the exercise of an option or
to receive shares under the Plan may be assigned, transferred, pledged or
otherwise disposed of in any way (other than by will, the laws of descent and
distribution, or as provided in Section 14 hereof) by the Participant.  Any such
attempt at assignment, transfer, pledge or other disposition shall be without
effect, except that the Administrator may treat such act as an election to
withdraw funds from an Offer Period in accordance with Section 10.

          16.  Use of Funds.  All payroll deductions received or held by the
               ------------
Company under the Plan may be used by the Company for any corporate purpose, and
the Company shall not be obligated to segregate such payroll deductions.

          17.  Reports.  Individual accounts will be maintained for each
               -------
Participant in the Plan.  Statements of account will be given to Participants at
least annually, which statements will set forth the amounts of payroll
deductions, the Purchase Price, the number of shares purchased and the remaining
cash balance, if any.

          18.  Adjustments Upon Changes in Capitalization; Corporate
               -----------------------------------------------------
Transactions.
------------

          (a)  Adjustments Upon Changes in Capitalization.  Subject to any
               ------------------------------------------
required action by the stockholders of the Company, the Reserves, the Purchase
Price, the maximum

                                       10
<PAGE>

number of shares that may be purchased in any Offer Period or Purchase Period,
as well as any other terms that the Administrator determines require adjustment
shall be proportionately adjusted for (i) any increase or decrease in the number
of issued shares of Common Stock resulting from a stock split, reverse stock
split, stock dividend, combination or reclassification of the Common Stock, (ii)
any other increase or decrease in the number of issued shares of Common Stock
effected without receipt of consideration by the Company, or (iii) as the
Administrator may determine in its discretion, any other transaction with
respect to Common Stock to which Section 424(a) of the Code applies; provided,
however that conversion of any convertible securities of the Company shall not
be deemed to have been "effected without receipt of consideration." Such
adjustment shall be made by the Administrator and its determination shall be
final, binding and conclusive. Except as the Administrator determines, no
issuance by the Company of shares of stock of any class, or securities
convertible into shares of stock of any class, shall affect, and no adjustment
by reason hereof shall be made with respect to, the Reserves and the Purchase
Price.

          (b)  Corporate Transactions.  In the event of a proposed Corporate
               ----------------------
Transaction, each option under the Plan shall be assumed by such successor
corporation or a parent or subsidiary of such successor corporation, unless the
Administrator, in the exercise of its sole discretion and in lieu of such
assumption, determines to shorten the Offer Period then in progress by setting a
new Exercise Date (the "New Exercise Date").  If the Administrator shortens the
Offer Period then in progress in lieu of assumption in the event of a Corporate
Transaction, the Administrator shall notify each Participant in writing at least
ten (10) business days prior to the New Exercise Date, that the Exercise Date
for the Participant's option has been changed to the New Exercise Date and that
either:
------

          (i)  the Participant's option will be exercised automatically on the
     New Exercise Date, unless prior to such date the Participant has withdrawn
     from the Offer Period as provided in Section 10; or

          (ii) the Company shall pay to the Participant on the New Exercise Date
     an amount in cash, cash equivalents, or property as determined by the
     Administrator that is equal to the difference in the Fair Market Value of
     the shares subject to the option and the Purchase Price due had the
     Participant's option been exercised automatically under Subsection (b)(i)
     above.

          For purposes of this Subsection, an option granted under the Plan
shall be deemed to be assumed if, in connection with the Corporate Transaction,
the option is replaced with a comparable option with respect to shares of
capital stock of the successor corporation or Parent thereof.  The determination
of option comparability shall be made by the Administrator prior to the
Corporate Transaction and its determination shall be final, binding and
conclusive on all persons.

          19.  Amendment or Termination.
               ------------------------

          (a)  The Administrator may at any time and for any reason terminate or
amend the Plan. Except as provided in Section 18, no such termination can affect
options previously

                                       11
<PAGE>

granted, provided that the Plan or any one or more Offer Periods may be
terminated by the Administrator on any Exercise Date or by the Administrator
establishing a new Exercise Date with respect to any Offer Period and/or any
Purchase Period then in progress if the Administrator determines that the
termination of the Plan or such one ore more Offer Periods is in the best
interests of the Company and its stockholders. Except as provided in Section 18
and this Section 19, no amendment may make any change in any option theretofore
granted which adversely affects the rights of any Participant without the
consent of affected Participants. To the extent necessary to comply with Section
423 of the Code (or any successor rule or provision or any other Applicable
Law), the Company shall obtain stockholder approval in such a manner and to such
a degree as required.

          (b)  Without stockholder consent and without regard to whether any
Participant rights may be considered to have been "adversely affected," the
Administrator shall be entitled to limit the frequency and/or number of changes
in the amount withheld during Offer Periods, change the length of Purchase
Periods within any Offer Period, determine the length of any future Offer
Period, determine whether future Offer Periods shall be consecutive or
overlapping, establish the exchange ratio applicable to amounts withheld in a
currency other than U.S. dollars, establish additional terms, conditions, rules
or procedures to accommodate the rules or laws of applicable foreign
jurisdictions, permit payroll withholding in excess of the amount designated by
a Participant in order to adjust for delays or mistakes in the Company's
processing of properly completed withholding elections, establish reasonable
waiting and adjustment periods and/or accounting and crediting procedures to
ensure that amounts applied toward the purchase of Common Stock for each
Participant properly correspond with amounts withheld from the Participant's
Compensation, and establish such other limitations or procedures as the
Administrator determines in its sole discretion advisable and which are
consistent with the Plan.

          20.  Notices.  All notices or other communications by a Participant to
               -------
the Company under or in connection with the Plan shall be deemed to have been
duly given when received in the form specified by the Administrator at the
location, or by the person, designated by the Administrator for the receipt
thereof.

          21.  Conditions Upon Issuance of Shares.  Shares shall not be issued
               ----------------------------------
with respect to an option unless the exercise of such option and the issuance
and delivery of such shares pursuant thereto shall comply with all Applicable
Laws and shall be further subject to the approval of counsel for the Company
with respect to such compliance. As a condition to the exercise of an option,
the Company may require the Participant to represent and warrant at the time of
any such exercise that the shares are being purchased only for investment and
without any present intention to sell or distribute such shares if, in the
opinion of counsel for the Company, such a representation is required by any of
the aforementioned Applicable Laws. In addition, no options shall be exercised
or shares issued hereunder before the Plan shall have been approved by
stockholders of the Company as provided in Section 23.

          22.  Term of Plan.  The Plan shall become effective upon the earlier
               ------------
to occur of its adoption by the Board or its approval by the stockholders of the
Company.  It shall continue in effect for a term of twenty (20) years unless
sooner terminated under Section 19.

                                       12
<PAGE>

          23.  Stockholder Approval.  Continuance of the Plan shall be subject
               --------------------
to approval by the stockholders of the Company within twelve (12) months before
or after the date the Plan is adopted.  Such stockholder approval shall be
obtained in the degree and manner required under Applicable Laws.

          24.  No Employment Rights.  The Plan does not, directly or indirectly,
               --------------------
create any right for the benefit of any employee or class of employees to
purchase any shares under the Plan, or create in any employee or class of
employees any right with respect to continuation of employment by the Company or
a Designated Parent or Subsidiary, and it shall not be deemed to interfere in
any way with such employer's right to terminate, or otherwise modify, an
employee's employment at any time.

          25.  No Effect on Retirement and Other Benefit Plans.  Except as
               -----------------------------------------------
specifically provided in a retirement or other benefit plan of the Company or a
Designated Parent or Subsidiary, participation in the Plan shall not be deemed
compensation for purposes of computing benefits or contributions under any
retirement plan of the Company or a Designated Parent or Subsidiary, and shall
not affect any benefits under any other benefit plan of any kind or any benefit
plan subsequently instituted under which the availability or amount of benefits
is related to level of compensation.  The Plan is not a "Retirement Plan" or
"Welfare Plan" under the Employee Retirement Income Security Act of 1974, as
amended.

          26.  Effect of Plan.  The provisions of the Plan shall, in accordance
               --------------
with its terms, be binding upon, and inure to the benefit of, all successors of
each Participant, including, without limitation, such Participant's estate and
the executors, administrators or trustees thereof, heirs and legatees, and any
receiver, trustee in bankruptcy or representative of creditors of such
Participant.

          27.  Governing Law.  The Plan is to be construed in accordance with
               -------------
and governed by the internal laws of the State of California (as permitted by
Section 1646.5 of the California Civil Code, or any similar successor provision)
without giving effect to any choice of law rule that would cause the application
of the laws of any jurisdiction other than the internal laws of the State of
California to the rights and duties of the parties, except to the extent the
internal laws of the State of California are superseded by the laws of the
United States.  Should any provision of the Plan be determined by a court of law
to be illegal or unenforceable, the other provisions shall nevertheless remain
effective and shall remain enforceable.

          28.  Dispute Resolution.  The provisions of this Section 28 (and as
               ------------------
restated in the Subscription Agreement) shall be the exclusive means of
resolving disputes arising out of or relating to the Plan.  The Company and the
Participant, or their respective successors (the "parties"), shall attempt in
good faith to resolve any disputes arising out of or relating to the Plan by
negotiation between individuals who have authority to settle the controversy.
Negotiations shall be commenced by either party by notice of a written statement
of the party's position and the name and title of the individual who will
represent the party.  Within thirty (30) days of the written notification, the
parties shall meet at a mutually acceptable time and place, and thereafter as
often as they reasonably deem necessary, to resolve the dispute.  If the dispute
has not been resolved by negotiation, the parties agree that any suit, action,
or proceeding arising out of or

                                       13
<PAGE>

relating to the Plan shall be brought in the United States District Court for
the Central District of California (or should such court lack jurisdiction to
hear such action, suit or proceeding, in a California state court in the County
of Los Angeles) and that the parties shall submit to the jurisdiction of such
court. The parties irrevocably waive, to the fullest extent permitted by law,
any objection the party may have to the laying of venue for any such suit,
action or proceeding brought in such court. THE PARTIES ALSO EXPRESSLY WAIVE ANY
RIGHT THEY HAVE OR MAY HAVE TO A JURY TRIAL OF ANY SUCH SUIT, ACTION OR
PROCEEDING. If any one or more provisions of this Section 28 shall for any
reason be held invalid or unenforceable, it is the specific intent of the
parties that such provisions shall be modified to the minimum extent necessary
to make it or its application valid and enforceable.

                                       14
<PAGE>

                                   Exhibit A

        American Pharmaceutical Partners, Inc. 2001 Employee Stock Purchase Plan
                                                          SUBSCRIPTION AGREEMENT

                                   Effective with the Offer Period beginning on:
                                   [_] (January 1, 200_)  or  [_] (July 1, 200_)

<TABLE>
<S>                                                                                     <C>
1. Personal Information (modify data requested as appropriate)

   Legal Name (Please Print)________________________________________________________    ___________________   ___________________
                                   (Last)            (First)             (MI)            Location              Department
   Street Address___________________________________________________________________    _________________________________________
                                                                                         Daytime Telephone
   City, State/Country, Zip__________________________________________________________   _________________________________________
                                                                                          E-Mail Address
   Social Security No. __ __ __ - __ __ - __ __ __   Employee I.D. No. ______________   _________________________________________
                                                                                           Manager                  Mgr. Location
</TABLE>

2. Eligibility   Any Employee whose customary employment is more than 20 hours
   per week and more than 5 months per calendar year, who has been an Employee
   for more than 3 business days and who does not hold (directly or indirectly)
   five percent (5%) or more of the combined voting power of the Company, a
   parent or a subsidiary, whether in stock or options to acquire stock is
   eligible to participate in the American Pharmaceutical Partners, Inc. 2001
   Employee Stock Purchase Plan (the "ESPP"); provided, however, that Employees
   who are subject to the rules or laws of a foreign jurisdiction that prohibit
   or make impractical the participation of such Employees in the ESPP are not
   eligible to participate.

3. Definitions  Each capitalized term in this Subscription Agreement shall have
   the meaning set forth in the ESPP.

4. Subscription  I hereby elect to participate in the ESPP and subscribe to
   purchase shares of the Company's Common Stock in accordance with this
   Subscription Agreement and the ESPP. I have received a complete copy of the
   ESPP and a prospectus describing the ESPP and understand that my
   participation in the ESPP is in all respects subject to the terms of the
   ESPP. The effectiveness of this Subscription Agreement is dependent on my
   eligibility to participate in the ESPP.

5. Payroll Deduction Authorization  I hereby authorize payroll deductions from
   my Compensation during the Offer Period in the percentage specified below
   (payroll reductions may not exceed 10% of Compensation nor $21,250 per
   calendar year):

   -----------------------------------------------------------------------------
    Percentage to be deducted (circle one) 1%  2% 3%  4%  5%  6%  7%  8%  9% 10%
   -----------------------------------------------------------------------------

6. ESPP Accounts and Purchase  I understand that all payroll deductions will be
   credited to my account Price under the ESPP. No additional payments may be
   made to my account. No interest will be credited on funds held in the account
   at any time including any refund of the account caused by withdrawal from the
   ESPP. All payroll deductions shall be accumulated for the purchase of Company
   Common Stock at the applicable Purchase Price determined in accordance with
   the ESPP.

7. Withdrawal and Changes in Payroll Deduction   I understand that I may
   discontinue my participation in the ESPP at any time prior to an Exercise
   Date as provided in Section 10 of the ESPP, but if I do not withdraw from the
   ESPP, any accumulated payroll deductions will be applied automatically to
   purchase Company Common Stock. I may increase or decrease the rate of my
   payroll deductions in whole percentage increments to not less than one
   percent (1%) on one occasion during any Purchase Period by completing and
   timely filing a Change of Status Notice. Any increase or decrease will be
   effective for the full payroll period occurring after three (3) business days
   from the Company's receipt of the Change of Status Notice.

8. Perpetual Subscription  I understand that this Subscription Agreement shall
   remain in effect for successive Offer Periods until I withdraw from
   participation in the ESPP, or termination of the ESPP.

                                      A-1
<PAGE>

9.   Taxes I have reviewed the ESPP prospectus discussion of the federal tax
     consequences of participation in the ESPP and consulted with tax
     consultants as I deemed advisable prior to my participation in the ESPP. I
     hereby agree to notify the Company in writing within thirty (30) days of
     any disposition (transfer or sale) of any shares purchased under the ESPP
     if such disposition occurs within two (2) years of the Enrollment Date (the
     first day of the Offer Period during which the shares were purchased) or
     within one (1) year of the Exercise Date (the date I purchased such
     shares), and I will make adequate provision to the Company for foreign,
     federal, state or other tax withholding obligations, if any, which arise
     upon the disposition of the shares. In addition, the Company may withhold
     from my Compensation any amount necessary to meet applicable tax
     withholding obligations incident to my participation in the ESPP, including
     any withholding necessary to make available to the Company any tax
     deductions or benefits contingent on such withholding.

10.  Dispute Resolution The provisions of this Section 10 and Section 28 of the
     ESPP shall be the exclusive means of resolving disputes arising out of or
     relating to the Plan. The Company and I, or our respective successors (the
     "parties"), shall attempt in good faith to resolve any disputes arising out
     of or relating to the Plan by negotiation between individuals who have
     authority to settle the controversy. Negotiations shall be commenced by
     either party by notice of a written statement of the party's position and
     the name and title of the individual who will represent the party. Within
     thirty (30) days of the written notification, the parties shall meet at a
     mutually acceptable time and place, and thereafter as often as they
     reasonably deem necessary, to resolve the dispute. If the dispute has not
     been resolved by negotiation, the Company and I agree that any suit,
     action, or proceeding arising out of or relating to the Plan shall be
     brought in the United States District Court for the Central District of
     California (or should such court lack jurisdiction to hear such action,
     suit or proceeding, in a California state court in the County of Los
     Angeles) and that we shall submit to the jurisdiction of such court. The
     Company and I irrevocably waive, to the fullest extent permitted by law,
     any objection we may have to the laying of venue for any such suit, action
     or proceeding brought in such court. THE COMPANY AND I ALSO EXPRESSLY WAIVE
     ANY RIGHT WE HAVE OR MAY HAVE TO A JURY TRIAL OF ANY SUCH SUIT, ACTION OR
     PROCEEDING. If any one or more provisions of this Section 10 or Section 28
     of the ESPP shall for any reason be held invalid or unenforceable, it is
     the specific intent of the Company and I that such provisions shall be
     modified to the minimum extent necessary to make it or its application
     valid and enforceable.

11.  Designation of Beneficiary In the event of my death, I hereby designate the
     following person or trust as my beneficiary to receive all payments and
     shares due to me under the ESPP:    [_] I am single        [_] I am married

<TABLE>
<S>                                                                           <C>
  Beneficiary (please print) ________________________________________________ Relationship to Beneficiary (if any)
                                    (Last)          (First)         (MI)
  Street Address ____________________________________________________________ ___________________________________
  City, State/Country, Zip __________________________________________________
</TABLE>

12.  Termination of ESPP I understand that the Company has the right,
     exercisable in its sole discretion, to amend or terminate the ESPP at any
     time, and a termination may be effective as early as an Exercise Date,
     including the establishment of an alternative date for an Exercise Date
     within each outstanding Offer Period.

     Date:__________________   Employee Signature:______________________________

                                               _________________________________

                                               spouse's signature (if
                                               beneficiary is other than spouse)

                                      A-2
<PAGE>

                                   Exhibit B

        American Pharmaceutical Partners, Inc. 2001 Employee Stock Purchase Plan
                                                         CHANGE OF STATUS NOTICE


______________________________________________________
Participant Name (Please Print)


______________________________________________________
Social Security Number

================================================================================

     Withdrawal From ESPP

     I hereby withdraw from the American Pharmaceutical Partners, Inc. 2001
     Employee Stock Purchase Plan (the "ESPP") and agree that my option under
     the applicable Offer Period will be automatically terminated and all
     accumulated payroll deductions credited to my account will be refunded to
     me or applied to the purchase of Common Stock depending on the alternative
     indicated below.  No further payroll deductions will be made for the
     purchase of shares in the applicable Offer Period and I shall be eligible
     to participate in a future Offer Period only by timely delivery to the
     Company of a new Subscription Agreement.

[_]  Withdrawal and Purchase of Common Stock

     Payroll deductions will terminate, but your account balance will be applied
     to purchase Common Stock on the next Exercise Date.  Any remaining balance
     will be refunded.

[_]  Withdrawal Without Purchase of Common Stock

     Entire account balance will be refunded to me and no Common Stock will be
     purchased on the next Exercise Date provided this notice is submitted to
     the Company ten (10) business days prior to the next Exercise Date.

================================================================================

[_]  Change in Payroll Deduction

     I hereby elect to change my rate of payroll deduction under the ESPP as
     follows (select one):

<TABLE>
--------------------------------------------------------------------------------
<S>                                     <C> <C> <C> <C> <C> <C> <C> <C> <C> <C>
Percentage to be Deducted (circle one)  1%  2%  3%  4%  5%  6%  7%  8%  9%  10%
--------------------------------------------------------------------------------
</TABLE>

     An increase or a decrease in payroll deduction will be effective for the
     first full payroll period commencing no fewer than three (3) business days
     following the Company's receipt of this notice, unless this change is
     processed more quickly.

================================================================================

                                      B-1
<PAGE>

================================================================================
[_]  Change of Beneficiary           [_] I am single         [_]  I am married

     This change of beneficiary shall terminate my previous beneficiary
     designation under the ESPP.  In the event of my death, I hereby designate
     the following person or trust as my beneficiary to receive all payments and
     shares due to me under the ESPP:

<TABLE>
<S>                                                                        <C>
    Beneficiary (please print) __________________________________________ Relationship to Beneficiary (if any)
                                    (Last)         (First)      (MI)

    Street Address ______________________________________________________ _____________________________________

    City, State/Country, Zip ____________________________________________
</TABLE>

================================================================================


 Date:_____________________ Employee Signature:_________________________________


                                               _________________________________
                                               spouse's signature (if new
                                               beneficiary is other than spouse)


                                      B-2
<PAGE>

                                   Exhibit C

        American Pharmaceutical Partners, Inc. 2001 Employee Stock Purchase Plan
                                                         CHANGE OF STATUS NOTICE
                        DURING FIRST PURCHASE PERIOD OF THE INITIAL OFFER PERIOD


__________________________________________
Participant Name (Please Print)


__________________________________________
Social Security Number


================================================================================
     Withdrawal From ESPP

     I hereby withdraw from the American Pharmaceutical Partners, Inc. 2001
     Employee Stock Purchase Plan (the "ESPP") and agree that my option under
     the applicable Offer Period will be automatically terminated.  No payroll
     deductions will be made for the purchase of shares in the initial Offer
     Period and I shall be eligible to participate in a future Offer Period only
     by timely delivery to the Company of a new Subscription Agreement.

[_]  Withdrawal Without Purchase by Direct Payment

     I elect not to purchase shares by direct payment during the first Purchase
     Period of the initial Offer Period.

================================================================================

[_]  Initiate Payroll Deduction During First Purchase Period of Initial Offer
     Period

     I hereby elect to initiate payroll deduction under the ESPP as follows
     (select one):

<TABLE>
--------------------------------------------------------------------------------
<S>                                     <C> <C> <C> <C> <C> <C> <C> <C> <C> <C>
Percentage to be Deducted (circle one)  1%  2%  3%  4%  5%  6%  7%  8%  9%  10%
--------------------------------------------------------------------------------
</TABLE>

     To the extent possible, the rate of payroll deduction will exceed the
     percentage indicated to yield the correct amount of withholding on the
     Exercise Date to cover payroll periods during which no withholding for
     participation in the Plan was made.

     I understand that this notice and payroll withholding rate shall remain in
     effect for successive Offer Periods until I withdraw from participation in
     the ESPP, change withholding rates, or the ESPP terminates.

     An increase or a decrease in payroll deduction or direct payment percentage
     will be effective for the first full payroll period commencing no fewer
     than three (3) business days following the Company's receipt of this
     notice, unless this change is processed more quickly.

================================================================================


                                      C-1
<PAGE>

================================================================================
Designation of Beneficiary

In the event of my death, I hereby designate the following person or trust as my
beneficiary to receive all payments and shares due to me under the ESPP:
[_] I am single     [_] I am married

<TABLE>
<S>                                                                        <C>
  Beneficiary (please print) ____________________________________________  Relationship to Beneficiary (if any)
                                 (Last)      (First)           (MI)

  Street Address ________________________________________________________  ____________________________________

  City, State/Country, Zip ______________________________________________
</TABLE>

================================================================================


  Date:___________________  Employee Signature:_________________________________


                                               _________________________________
                                               spouse's signature (if new
                                               beneficiary is other than spouse)


                                      C-2