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                                                                   EXHIBIT 10.21

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                                Warrant Agreement

                            Dated as of April 9, 2003

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      WARRANT AGREEMENT, dated as of April 9, 2003, between BioTime, Inc., a
California corporation (the "Company"), and the persons named on Exhibit A (the
"Lenders").

      The Lenders have granted the Company the right to pay in Common Stock
rather than cash due (the "PIK Right") interest due during August 2003 and
February 2004 on the Company's Series 2001-A Debentures (the "Debentures"). The
Company proposes to issue Common Stock Purchase Warrants, as hereinafter
described (the "Warrants"), to purchase up to an aggregate of 223,331 of its
Common Shares, no par value (the "Common Stock") (the shares of Common Stock
issuable upon exercise of the Warrants being referred to herein as the "Warrant
Shares"), to the Lenders in consideration of the grant of the PIK Right. Any
shares of Common Stock issued by the Company to Lenders in lieu of cash interest
on the Debentures pursuant to the PIK Right are referred to in this Agreement as
"PIK Shares."

      In consideration of the foregoing and for the purpose of defining the
terms and provisions of the Warrants and the respective rights and obligations
thereunder of the Company and each registered owner of a Warrant, Warrant
Shares, or PIK Shares (the "Holder"), the Company and the Lenders hereby agree
as follows:

      Section 1. Issuance of Warrants; Term of Warrants. Concurrently with the
execution and delivery of this Agreement, the Company is issuing and delivering
to each Lender a Warrant to purchase a number of Warrant Shares determined by
dividing the amount of interest due on their respective Debentures during August
2003 and February 2004 (without regard to any late fee, default rate or similar
provision) by $1.50. The Warrant shall be represented by a certificate in
substantially the form of Exhibit B hereto. Subject to the terms of this
Agreement, a Holder of any of such Warrant (including any Warrants into which a
Warrant may be divided) shall have the right, which may be exercised at any time
prior to 5:00 p.m., New York Time on April 1, 2006 (the "Expiration Date"), to
purchase from the Company the number of fully paid and nonassessable Warrant
Shares which the Holder may at the time be entitled to purchase upon exercise of
any of such Warrant.

      Section 2. Form of Warrant. The text of the Warrants and of the Purchase
Form shall be substantially as set forth in Exhibit B attached hereto. The price
per Warrant Share and the number of Warrant Shares issuable upon exercise of
each Warrant are subject to adjustment upon the occurrence of certain events,
all as hereinafter provided. The Warrants shall be executed on behalf of the
Company by its Chairman of the Board, President or one of its Vice Presidents,
under its corporate seal reproduced thereon attested by its Secretary or any
Assistant Secretary. The signature of any such officers on the Warrants may be
manual or facsimile, provided, however, that the signature of any such officers
must be manual until such time as a warrant agent is appointed.


      2.1 Signatures; Date of Warrants. Warrants bearing the manual or facsimile
signatures of individuals who were at any time the proper officers of the
Company shall bind the Company, notwithstanding that such individuals or any one
of them shall have ceased to hold such offices prior to the delivery of such
Warrants or did not hold such offices on the date of this Agreement. In the
event that the Company shall appoint a warrant agent to act on its behalf in
connection with the division, transfer, exchange or exercise of Warrants, the
Warrants issued after


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the date of such appointment shall be dated as of the date of countersignature
thereof by the warrant agent upon division, exchange, substitution or transfer.
Until such time as the Company shall appoint a warrant agent, Warrants shall be
dated as of the date of execution thereof by the Company either upon initial
issuance or upon division, exchange, substitution or transfer.

      2.2 Countersignature of Warrants. In the event that the Company shall
appoint a warrant agent to act on its behalf in connection with the division,
transfer, exchange or exercise of Warrants, the Warrants issued after the date
of such appointment shall be countersigned by the warrant agent (or any
successor to the warrant agent then acting as warrant agent) and shall not be
valid for any purpose unless so countersigned. Warrants may be countersigned,
however, by the warrant agent (or by its successor as warrant agent hereunder)
and may be delivered by the warrant agent, notwithstanding that the persons
whose manual or facsimile signatures appear thereon as proper officers of the
Company shall have ceased to be such officers at the time of such
countersignature, issuance or delivery. The warrant agent (if so appointed)
shall, upon written instructions of the Chairman of the Board, the President, an
Executive or Senior Vice President, the Treasurer or the Controller of the
Company, countersign, issue and deliver the Warrants and shall countersign and
deliver Warrants as otherwise provided in this Agreement.

      Section 3. Exercise of Warrants; Listing.

      3.1 Exercise of Warrants. A Warrant may be exercised upon surrender of the
certificate or certificates evidencing the Warrants to be exercised, together
with the form of election to purchase on the reverse thereof duly filled in and
signed, which signature shall be guaranteed by a bank or trust company or a
broker or dealer which is a member of the National Association of Securities
Dealers, Inc., to the Company at its principal office (or if appointed, the
principal office of the warrant agent) and upon payment of the Warrant Price (as
defined in and determined in accordance with the provisions of Section 4 and
Section 10) to the Company (or if appointed, to the warrant agent for the
account of the Company), for the number of Warrant Shares in respect of which
such Warrants are then exercised. Payment of the aggregate Warrant Price
(defined in Section 4 herein) shall be made in cash or by certified or bank
cashier's check or by delivery of Debentures in such amount (including principal
and accrued interest). In the event that the principal amount of Debentures
delivered as payment of the Warrant Price exceeds the Warrant Price, the Company
shall issue and deliver to the Holder a new Debenture in the amount not applied
toward the Warrant Price.


      (a) Subject to Section 5, upon the surrender of the Warrant and payment of
the Warrant Price as aforesaid, the Company (or if appointed, the warrant agent)
shall promptly cause to be issued and delivered to or upon the written order of
the Holder and in such name or names as the Holder may designate, a certificate
or certificates for the number of full Warrant Shares so purchased upon the
exercise of such Warrant, together with cash, as provided in Section 12, in
respect of any fractional Warrant Shares otherwise issuable upon such surrender.
Such certificate or certificates shall be deemed to have been issued and any
person so designated to be named therein shall be deemed to have become a holder
of record of such Warrant Shares as of the date of the surrender of such
Warrants and payment of the Warrant Price, as aforesaid. The rights of purchase
represented by the Warrant shall be exercisable, at the election of the Holder
thereof, either in full or

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from time to time in part and, in the event that a certificate evidencing the
Warrant is exercised in respect of less than all of the Warrant Shares
purchasable on such exercise at any time prior to the date of expiration of the
Warrant, a new certificate evidencing the unexercised portion of the Warrant
will be issued, and the warrant agent (if so appointed) is hereby irrevocably
authorized to countersign and to deliver the required new Warrant certificate or
certificates pursuant to the provisions of this Section 3 and Section 2.2, and
the Company, whenever required by the warrant agent (if appointed), will supply
the warrant agent with Warrant certificates duly executed on behalf of the
Company for such purpose.

      3.2 Listing of Shares on Securities Exchange; Exchange Act Registration.
The Company will promptly use its best efforts to cause the Warrant Shares to be
listed, subject to official notice of issuance, on all national securities
exchanges on which the Common Stock is listed and whose rules and regulations
require such listing, as soon as possible following the date hereof. The Company
will promptly notify the Holders in the event that the Company plans to register
the Warrants with the Securities and Exchange Commission under the Securities
Exchange Act of 1934, as amended (the "Exchange Act").

      Section 4. Warrant Price. Subject to any adjustments required by Section
10, the price per share at which Warrant Shares shall be purchasable upon
exercise of a Warrant (as to any particular Warrant, the "Warrant Price") shall
be one dollar and fifty-cents ($1.50) per share.

      Section 5. Payment of Taxes. The Company will pay all documentary stamp
taxes, if any, attributable to the initial issuance of Warrant Shares upon the
exercise of Warrants; provided, however, that the Company shall not be required
to pay any tax or taxes which may be payable in respect of any transfer involved
in the issue or delivery of any Warrant or certificates for Warrant Shares in a
name other than that of the registered Holder of such Warrants.

      Section 6. Redemption of Warrants.

      6.1 Right to Redeem. The Warrants may be redeemed by the Company, at its
election, at any time if (a) a registration statement under Section 18.1 or a
registration statement under Section 18.2 that includes Warrants and Warrant
Shares is then effective under the Securities Act of 1933, as amended, and (b)
the closing price of the Common Stock on a national securities exchange
(including the Nasdaq Stock Market National Market System), or the average bid
price as quoted in Nasdaq Stock Market if the Common Shares are not listed on a
national securities exchange, equals or exceeds 200% of the Warrant Price for
any twenty (20) consecutive trading days ending not more than twenty (20) days
prior to the date of the notice given pursuant to Section 6.2.

      6.2 Notice of Redemption. Notice of proposed redemption of the Warrants
shall be sent by or on behalf of the Company, by first class mail, postage
prepaid, to the Holders of record of the Warrants at the addresses of such
Holders appearing in the records of the Company or the warrant agent, if any.
Such notice shall be sent not less than twenty (20) days prior to the date fixed
by the Company for redemption (the "Redemption Date"). Such notice shall notify
the Holder of the Warrants that the Company will redeem the Warrants, and shall
state (i) the date of redemption, (ii)

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the redemption price, (iii) the place or places at which the redemption price
shall be paid upon presentation and surrender of the Warrants, and (iv) the name
and address of the warrant agent, if any, and the name and address of any bank
or trust company appointed by the Company to receive and disburse the redemption
price.

      6.3 Effect of Redemption. From and after the Redemption Date, the Warrants
shall no longer be deemed outstanding and all rights of the Holder of the
Warrants shall cease and terminate, except for the right of the registered
Holder to receive payment of the redemption price of five cents ($0.05) per
Warrant Share upon presentation and surrender of the Warrants.

      6.4 Abatement of Redemption. The Redemption Date shall abate, and the
notice of redemption shall be of no effect, if the closing price or average bid
price of the Common Stock, as applicable under Section 6.1, does not equal or
exceed 120% of the Warrant Price on the Redemption Date and each of the five
trading days immediately preceding the Redemption Date, but the Company shall
have the right to redeem the Warrants at a future date if the conditions set
forth in Section 6.1 are subsequently met and a new notice setting a new
Redemption Date is sent to Warrant holders as provided in Section 6.2.

      Section 7. Transferability of Warrants.


      7.1 Registration. Each Warrant shall be numbered and shall be registered
on the books of the Company (the "Warrant Register") as issued. The Company and
the warrant agent (if appointed) shall be entitled to treat the Holder of any
Warrant as the owner in fact thereof for all purposes and shall not be bound to
recognize any equitable or other claim or interest in such Warrant on the part
of any other person, and shall not be liable for any registration of transfer of
any Warrant which is registered or to be registered in the name of a fiduciary
or the nominee of a fiduciary upon the instruction of such fiduciary, unless
made with the actual knowledge that a fiduciary or nominee is committing a
breach of trust in requesting such registration or transfer, or with such
knowledge of such facts that its participation therein amounts to bad faith.
Each Warrant shall initially be registered in the name of the Lender to whom it
is originally issued.

      7.2 Restrictions on Exercise and Transfer. The Warrants may not be
exercised, sold, pledged, hypothecated, transferred or assigned, in whole or in
part, unless a registration statement under the Securities Act of 1933, as
amended (the "Act"), and under any applicable state securities laws is effective
therefor or, an exemption from such registration is then available. Any
exercise, sale, pledge, hypothecation, transfer, or assignment in violation of
the foregoing restriction shall be deemed null and void and of no binding
effect. The Company shall be entitled to obtain, as a condition precedent to its
issuance of any certificates representing Warrant Shares or any other securities
issuable upon any exercise of a Warrant, a letter or other instrument from the
Holder containing such covenants, representations or warranties by such Holder
as reasonably deemed necessary by Company to effect compliance by the Company
with the requirements of applicable federal and/or state securities laws.

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      7.3 Transfer. Subject to Section 7.2, the Warrants shall be transferable
only on the Warrant Register upon delivery thereof duly endorsed by the Holder
or by his duly authorized attorney or representative, or accompanied by proper
evidence of succession, assignment or authority to transfer, which endorsement
shall be guaranteed by a bank or trust company or a broker or dealer which is a
member of the National Association of Securities Dealers, Inc. In all cases of
transfer by an attorney, the original power of attorney, duly approved, or a
copy thereof, duly certified, shall be deposited and remain with the Company (or
the warrant agent, if appointed). In case of transfer by executors,
administrators, guardians or other legal representatives, duly authenticated
evidence of their authority shall be produced, and may be required to be
deposited and remain with the Company (or the warrant agent, if appointed) in
its discretion. Upon any registration of transfer, the Company shall execute and
deliver (or if appointed, the warrant agent shall countersign and deliver) a new
Warrant or Warrants to the persons entitled thereto.

      Section 8. Exchange of Warrant Certificates. Each Warrant certificate may
be exchanged, at the option of the Holder thereof, for another Warrant
certificate or Warrant certificates in different denominations entitling the
Holder or Holders thereof to purchase a like aggregate number of Warrant Shares
as the certificate or certificates surrendered then entitle each Holder to
purchase. Any Holder desiring to exchange a Warrant certificate or certificates
shall make such request in writing delivered to the Company at its principal
office (or, if a warrant agent is appointed, the warrant agent at its principal
office) and shall surrender, properly endorsed, the certificate or certificates
to be so exchanged. Thereupon, the Company (or, if appointed, the warrant agent)
shall execute and deliver to the person entitled thereto a new Warrant
certificate or certificates, as the case may be, as so requested, in such name
or names as such Holder shall designate.

      Section 9. Mutilated or Missing Warrants. In case any of the certificates
evidencing the Warrants shall be mutilated, lost, stolen or destroyed, the
Company may in its discretion issue and deliver (and, if appointed, the warrant
agent shall countersign and deliver) in exchange and substitution for and upon
cancellation of the mutilated Warrant certificate, or in lieu of and
substitution for the Warrant certificate lost, stolen or destroyed, a new
Warrant certificate of like tenor, but only upon receipt of evidence reasonably
satisfactory to the Company and the warrant agent (if so appointed) of such
loss, theft or destruction of such Warrant and an indemnity or bond, if
requested, also reasonably satisfactory to them. An applicant for such a
substitute Warrant certificate shall also comply with such other reasonable
regulations and pay such other reasonable charges as the Company (or the warrant
agent, if so appointed) may prescribe.

      Section 10. Adjustment of Warrant Price and Number of Warrant Shares. The
number and kind of securities purchasable upon the exercise of each Warrant and
the Warrant Price shall be subject to adjustment from time to time upon the
happening of certain events, as hereinafter defined.

      10.1 Adjustments. The number of Warrant Shares purchasable upon the
exercise of each Warrant and the Warrant Price shall be subject to adjustment as
follows:

            (a) In the event that the Company shall (i) pay a dividend in shares
      of Common Stock or make a distribution in shares of Common Stock, (ii)
      subdivide its outstanding

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      shares of Common Stock, (iii) combine its outstanding shares of Common
      Stock into a smaller number of shares of Common Stock or (iv) reclassify
      or change (including a change to the right to receive, or a change into,
      as the case may be (other than with respect to a merger or consolidation
      pursuant to the exercise of appraisal rights), shares of stock, other
      securities, property, cash or any combination thereof) its Common Stock
      (including any such reclassification or change in connection with a
      consolidation or merger in which the Company is the surviving
      corporation), the number of Warrant Shares purchasable upon exercise of
      each Warrant immediately prior thereto shall be adjusted so that the
      Holder of each Warrant shall be entitled to receive the kind and number of
      Warrant Shares or other securities of the Company or other property which
      he would have owned or have been entitled to receive after the happening
      of any of the events described above, had such Warrant been exercised
      immediately prior to the happening of such event or any record date with
      respect thereto. An adjustment made pursuant to this paragraph (a) shall
      become effective immediately after the effective date of such event
      retroactive to the record date, if any, for such event.

            (b) In case the Company shall issue rights, options or warrants to
      all holders of its outstanding Common Stock, without any charge to such
      holders, entitling them to subscribe for or purchase shares of Common
      Stock at a price per share which is lower at the record date mentioned
      below than the then current market price per share of Common Stock (as
      defined in paragraph (d) below), the number of Warrant Shares thereafter
      purchasable upon the exercise of each Warrant shall be determined by
      multiplying the number of Warrant Shares theretofore purchasable upon
      exercise of each Warrant by a fraction, of which the numerator shall be
      the number of shares of Common Stock outstanding on the date of issuance
      of such rights, options or warrants plus the number of additional shares
      of Common Stock offered for subscription or purchase in connection with
      such rights, options or warrants, and of which the denominator shall be
      the number of shares of Common Stock outstanding on the date of issuance
      of such rights, options or warrants plus the number of shares which the
      aggregate offering price of the total number of shares of Common Stock so
      offered would purchase at the current market price per share of Common
      Stock at such record date. Such adjustment shall be made whenever such
      rights, options or warrants are issued, and shall become effective
      immediately after the record date for the determination of stockholders
      entitled to receive such rights, options or warrants.

            (c) In case the Company shall distribute to all holders of its
      shares of Common Stock, (including any distribution made in connection
      with a merger in which the Company is the surviving corporation),
      evidences of its indebtedness or assets (excluding cash, dividends or
      distributions payable out of consolidated earnings or earned surplus and
      dividends or distributions referred to in paragraph (a) above) or rights,
      options or warrants, or convertible or exchangeable securities containing
      the right to subscribe for or purchase shares of Common Stock (excluding
      those referred to in paragraph (b) above), then in each case the number of
      Warrant Shares thereafter purchasable upon the exercise of each Warrant
      shall be determined by multiplying the number of Warrant Shares
      theretofore purchasable upon the exercise of each Warrant by a fraction,
      of which the numerator shall be the then current market price per share of
      Common Stock (as defined in paragraph (d) below) on the date of such
      distribution, and of which the denominator shall be the then current
      market price per share of Common Stock, less the then fair value (as
      determined by the Board of Directors of the Company or, in the case of
      Warrants held by the Lender, an

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      independent investment banker which shall be mutually agreeable to the
      parties, whose determination, in each case, shall be conclusive) of the
      portion of the assets or evidences of indebtedness so distributed or of
      such subscription rights, options or warrants, or of such convertible or
      exchangeable securities applicable to one share of Common Stock. Such
      adjustment shall be made whenever any such distribution is made, and shall
      become effective on the date of distribution retroactive to the record
      date for the determination of shareholders entitled to receive such
      distribution.

            (d) For the purpose of any computation under paragraphs (b) and (c)
      of this Section 10.1, the current market price per share of Common Stock
      at any date shall be the average of the daily last sale prices for the 20
      consecutive trading days ending one trading day prior to the date of such
      computation. The closing price for each day shall be the last reported
      sales price regular way or, in case no such reported sale takes place on
      such day, the average of the closing bid and asked prices regular way for
      such day, in each case on the principal national securities exchange on
      which the shares of Common Stock are listed or admitted to trading or, if
      not so listed or admitted to trading, the last sale price of the Common
      Stock on the Nasdaq Stock Market or any comparable system. If the current
      market price of the Common Stock cannot be so determined, the Board of
      Directors of the Company shall reasonably determine the current market
      price on the basis of such quotations as are available.

            (e) No adjustment in the number of Warrant Shares purchasable
      hereunder shall be required unless such adjustment would require an
      increase or decrease of at least one percent (1%) in the number of Warrant
      Shares purchasable upon the exercise of each Warrant; provided, however,
      that any adjustments which by reason of this paragraph (e) are not
      required to be made shall be carried forward and taken into account in the
      determination of any subsequent adjustment. All calculations shall be made
      with respect to the number of Warrant Shares purchasable hereunder, to the
      nearest tenth of a share and with respect to the Warrant Price payable
      hereunder, to the nearest whole cent.

            (f) Whenever the number of Warrant Shares purchasable upon the
      exercise of each Warrant is adjusted, as herein provided, the Warrant
      Price payable upon exercise of each Warrant shall be adjusted by
      multiplying such Warrant Price immediately prior to such adjustment by a
      fraction, of which the numerator shall be the number of Warrant Shares
      purchasable upon the exercise of each Warrant immediately prior to such
      adjustment, and of which the denominator shall be the number of Warrant
      Shares purchasable immediately thereafter.

            (g) No adjustment in the number of Warrant Shares purchasable upon
      the exercise of each Warrant need be made under paragraphs (b) and (c) if
      the Company issues or distributes to each Holder of Warrants the rights
      options, warrants, or convertible or exchangeable securities, or evidences
      of indebtedness or assets referred to in those paragraphs which each
      Holder of Warrants would have been entitled to receive had the Warrants
      been exercised prior to the happening of such event or the record date
      with respect thereto. No adjustment need be made for a change in the par
      value of the Warrant Shares.

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            (h) For the purpose of this Section 10.1, the term "shares of Common
      Stock" shall mean (i) the class of stock designated as the Common Stock of
      the Company at the date of this Agreement, or (ii) any other class of
      stock resulting from successive changes or reclassifications of such
      shares consisting solely of changes in par value, or from par value to no
      par value, or from no par value to par value. In the event that at any
      time, as a result of an adjustment made pursuant to paragraph (a) above,
      the Holders shall become entitled to purchase any securities of the
      Company other than shares of Common Stock, thereafter the number of such
      other shares so purchasable upon exercise of each Warrant and the Warrant
      Price of such shares shall be subject to adjustment from time to time in a
      manner and on terms as nearly equivalent as practicable to the provisions
      with respect to the Warrant Shares contained in paragraphs (a) through
      (i), inclusive, and the provisions of Section 3 and Section 10.2 through
      Section 10.5, inclusive, with respect to the Warrant Shares, shall apply
      on like terms to any such other securities.

            (i) Upon the expiration of any rights, options, warrants or
      conversion or exchange privileges, if any thereof shall not have been
      exercised, the Warrant Price and the number of Warrant Shares purchasable
      upon the exercise of each Warrant shall, upon such expiration, be
      readjusted and shall thereafter be such as it would have been had it been
      originally adjusted (or had the original adjustment not been required, as
      the case may be) as if (A) the only shares of Common Stock so issued were
      the shares of Common Stock, if any, actually issued or sold upon the
      exercise of such rights, options, warrants or conversion or exchange
      rights and (B) such shares of Common Stock, if any, were issued or sold
      for the consideration actually received by the Company upon such exercise
      plus the aggregate consideration, if any, actually received by the Company
      for the issuance, sale or grant of all such rights, options, warrants or
      conversion or exchange rights whether or not exercised.

      10.2 Voluntary Adjustment by the Company. The Company may at its option,
at any time during the term of the Warrants, reduce the then current Warrant
Price to any amount deemed appropriate by the Board of Directors of the Company.

      10.3 Notice of Adjustment. Whenever the number of Warrant Shares
purchasable upon the exercise of each Warrant or the Warrant Price of such
Warrant Shares is adjusted, as herein provided, the Company shall, or in the
event that a warrant agent is appointed, the Company shall cause the warrant
agent promptly to, mail by first class, postage prepaid, to each Holder notice
of such adjustment or adjustments. Such notice shall set forth the number of
Warrant Shares purchasable upon the exercise of each Warrant and the Warrant
Price of such Warrant Shares after such adjustment, setting forth a brief
statement of the facts requiring such adjustment and setting forth the
computation by which such adjustment was made.

      10.4 No Adjustment for Dividends. Except as provided in Section 10.1, no
adjustment in respect of any dividends shall be made during the term of a
Warrant or upon the exercise of a Warrant.

      10.5 Preservation of Purchase Rights Upon Merger, Consolidation, etc. In
case of any consolidation of the Company with or merger of the Company into
another corporation or in case

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of any sale, transfer or lease to another corporation of all or substantially
all the property of the Company, the Company or such successor or purchasing
corporation, as the case may be, shall execute an agreement that each Holder
shall have the right thereafter, upon such Holder's election, either (i) upon
payment of the Warrant Price in effect immediately prior to such action, to
purchase upon exercise of each Warrant the kind and amount of shares and other
securities and property (including cash) which he would have owned or have been
entitled to receive after the happening of such consolidation, merger, sale,
transfer or lease had such Warrant been exercised immediately prior to such
action (such shares and other securities and property (including cash) being
referred to as the "Sale Consideration") or (ii) to receive, in cancellation of
such Warrant (and in lieu of paying the Warrant price and exercising such
Warrant), the Sale Consideration less a portion thereof having a fair market
value (as reasonably determined by the Company) equal to the Warrant Price (it
being understood that, if the Sale Consideration consists of more than one type
of shares, other securities or property, the amount of each type of shares,
other securities or property to be received shall be reduced proportionately);
provided, however, that no adjustment in respect of dividends, interest or other
income on or from such shares or other securities and property shall be made
during the term of a Warrant or upon the exercise of a Warrant. The Company
shall mail by first class mail, postage prepaid, to each Holder, notice of the
execution of any such agreement. Such agreement shall provide for adjustments,
which shall be as nearly equivalent as may be practicable to the adjustments
provided for in this Section 10. The provisions of this paragraph shall
similarly apply to successive consolidations, mergers, sales, transfers or
leases. The warrant agent (if appointed) shall be under no duty or
responsibility to determine the correctness of any provisions contained in any
such agreement relating to the kind or amount of shares of stock or other
securities or property receivable upon exercise of Warrants or with respect to
the method employed and provided therein for any adjustments and shall be
entitled to rely upon the provisions contained in any such agreement.

      10.6 Statement on Warrants. Irrespective of any adjustments in the Warrant
Price or the number or kind of shares purchasable upon the exercise of the
Warrants, Warrants issued before or after such adjustment may continue to
express the same price and number and kind of shares as are stated in the
Warrants initially issuable pursuant to this Agreement.

      Section 11. Reservation of Warrant Shares; Purchase and Cancellation of
      Warrants.

      11.1 Reservation of Warrant Shares. There have been reserved, and the
Company shall at all times keep reserved, out of its authorized Common Stock, a
number of shares of Common Stock sufficient to provide for the exercise of the
rights of purchase represented by the outstanding Warrants and any additional
Warrants issuable hereunder. The Transfer Agent for the Common Stock and every
subsequent transfer agent for any shares of the Company's capital stock issuable
upon the exercise of any of the rights of purchase aforesaid will be irrevocably
authorized and directed at all times to reserve such number of authorized shares
as shall be required for such purpose. The Company will keep a copy of this
Agreement on file with the Transfer Agent for the Common Stock and with every
subsequent transfer agent for any shares of the Company's capital stock issuable
upon the exercise of the rights of purchase represented by the Warrants. The
warrant agent, if appointed, will be irrevocably authorized to requisition from
time to time from such Transfer Agent the stock certificates required to honor
outstanding Warrants upon exercise thereof in


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accordance with the terms of this Agreement. The Company will supply such
Transfer Agent with duly executed stock certificates for such purposes and will
provide or otherwise make available any cash which may be payable as provided in
Section 12. The Company will furnish such Transfer Agent a copy of all notices
of adjustments and certificates related thereto, transmitted to each Holder
pursuant to Section 10.3.

      11.2 Purchase of Warrants by the Company. The Company shall have the
right, except as limited by law, other agreements or herein, with the consent of
the Holder, to purchase or otherwise acquire Warrants at such times, in such
manner and for such consideration as it may deem appropriate.

      11.3 Cancellation of Warrants. In the event the Company shall purchase or
otherwise acquire Warrants, the same shall thereupon be cancelled and retired.
The warrant agent (if so appointed) shall cancel any Warrant surrendered for
exchange, substitution, transfer or exercise in whole or in part.

      Section 12. Fractional Interests. The Company shall not be required to
issue fractional Warrant Shares on the exercise of Warrants. If more than one
Warrant shall be presented for exercise in full at the same time by the same
Holder, the number of full Warrant Shares which shall be issuable upon the
exercise thereof shall be computed on the basis of the aggregate number of
Warrant Shares purchasable on exercise of the Warrants so presented. If any
fraction of a Warrant Share would, except for the provisions of this Section 12,
be issuable on the exercise of any Warrant (or specified portion thereof), the
Company shall pay an amount in cash equal to the average of the daily closing
sale prices (determined in accordance with paragraph (d) of Section 10.1) per
share of Common Stock for the 20 consecutive trading days ending one trading day
prior to the date the Warrant is presented for exercise, multiplied by such
fraction.

      Section 13. No Rights as Shareholders; Notices to Holders. Nothing
contained in this Agreement or in any of the Warrants shall be construed as
conferring upon the Holders or their transferees the right to vote or to receive
dividends or to consent or to receive notice as shareholders in respect of any
meeting of shareholders for the election of directors of the Company or any
other matter, or any rights whatsoever as shareholders of the Company. If,
however, at any time prior to the expiration of the Warrants and prior to their
exercise, any of the following events shall occur:

            (a) the Company shall declare any dividend payable in any securities
      upon its shares of Common Stock or make any distribution (other than a
      regular cash dividend, as such dividend may be increased from time to
      time, or a dividend payable in shares of Common Stock) to the holders of
      its shares of Common Stock; or

            (b) the Company shall offer to the holders of its shares of Common
      Stock on a pro rata basis any cash, additional shares of Common Stock or
      other securities of the Company or any right to subscribe for or purchase
      any thereof; or

                                       10
<PAGE>

            (c) a dissolution, liquidation or winding up of the Company (other
      than in connection with a consolidation, merger, sale, transfer or lease
      of all or substantially all of its property, assets, and business as an
      entirety) shall be proposed,

then in any one or more of said events the Company shall (i) give notice in
writing of such event as provided in Section 15 and (ii) if the Warrants have
been registered pursuant to the Act, cause notice of such event to be published
once in The Wall Street Journal (national edition), such giving of notice and
publication to be completed at least 10 days prior to the date fixed as a record
date or the date of closing the transfer books for the determination of the
stockholders entitled to such dividend, distribution, or subscription rights or
for the determination of stockholders entitled to vote on such proposed
dissolution, liquidation or winding up or the date of expiration of such offer.
Such notice shall specify such record date or the date of closing the transfer
books or the date of expiration, as the case may be. Failure to publish, mail or
receive such notice or any defect therein or in the publication or mailing
thereof shall not affect the validity of any action in connection with such
dividend, distribution or subscription rights, or such proposed dissolution,
liquidation or winding up, or such offer.

      Section 14. Appointment of Warrant Agent. At such time as the Company
shall register Warrants under the Act, the Company shall appoint a warrant agent
to act on behalf of the Company in connection with the issuance, division,
transfer and exercise of Warrants. At such time as the Company appoints a
warrant agent, the Company shall enter into a new Warrant Agreement with the
warrant agent pursuant to which all new Warrants will be issued upon
registration of transfer or division, which will reflect the appointment of the
warrant agent, as well as additional customary provisions as shall be reasonably
requested by the warrant agent in connection with the performance of its duties.
In the event that a warrant agent is appointed, the Company shall (i) promptly
notify the Holders of such appointment and the place designated for transfer,
exchange and exercise of the Warrants, and (ii) take such steps as are necessary
to insure that Warrants issued prior to such appointment may be exchanged for
Warrants countersigned by the warrant agent.

      Section 15. Notices; Principal Office. Any notice pursuant to this
Agreement by the Company or by any Holder to the warrant agent (if so
appointed), or by the warrant agent (if so appointed) or by any Holder to the
Company, shall be in writing and shall be delivered in person, or mailed first
class, postage prepaid (a) to the Company, at its office, Attention: President
or (b) to the warrant agent, at its offices as designated at the time the
warrant agent is appointed. The address of the principal office of the Company
is 935 Pardee Street, Berkeley, California 94710. Any notice mailed pursuant to
this Agreement by the Company or the warrant agent to the Holders shall be in
writing and shall be mailed first class, postage prepaid, or otherwise
delivered, to such Holders at their respective addresses on the books of the
Company or the warrant agent, as the case may be. Each party hereto and any
Holder may from time to time change the address to which notices to it are to be
delivered or mailed hereunder by notice to the other party.

      Section 16. Successors. Except as expressly provided herein to the
contrary, all the covenants and provisions of this Agreement by or for the
benefit of the Company and the Lender shall bind and inure to the benefit of
their respective successors and permitted assigns hereunder.


                                       11
<PAGE>

      Section 17. Merger or Consolidation of the Company. The Company will not
merge or consolidate with or into, or sell, transfer or lease all or
substantially all of its property to, any other corporation unless the successor
or purchasing corporation, as the case may be (if not the Company), shall
expressly assume, by supplemental agreement, the due and punctual performance
and observance of each and every covenant and condition of this Agreement to be
performed and observed by the Company.

      Section 18. Registration Rights.

      18.1 Filing of Registration Statement. The Company agrees, at its expense,
to file a registration statement with the Securities and Exchange Commission to
register under the Act the Warrants and the Warrant Shares and any PIK Shares,
and to take such other actions as may be necessary to allow the Warrants, the
Warrant Shares and the PIK Shares to be freely tradable, without restrictions,
in compliance with all regulatory requirements. Such registration statement
shall be filed promptly after the February 2004 interest payment date of the
Debentures, and the Company will use its best efforts to cause the registration
statement to become effective within 120 days after the filing date. The Company
will make all filings required under applicable state securities or "blue sky"
laws so that the Warrants, Warrant Shares and PIK Shares being registered shall
be registered or qualified for sale under the securities or blue sky laws of
such jurisdictions as shall be reasonably appropriate for distribution of the
Warrants, Warrant Shares, and PIK Shares covered by the registration statement.
The registration statement shall be a "shelf" registration pursuant to Rule 415
(or similar rule that may be adopted by the Securities and Exchange Commission)
and shall provide that each Holder's plan of distribution is to offer and sell
Warrant Shares and PIK Shares from time to time at market prices or prices
related to market prices; provided, that the registration statement may be
amended to provide for an underwritten public offering of Warrant Shares and PIK
Shares if the Holders submit to the Company a written notice to such effect with
a copy of the applicable underwriting documents and such other relevant
information concerning the offering as the Company may request. The Company
shall keep such registration statement effective until the earlier of (a)
completion of the distribution or distributions being made pursuant thereto, and
(b) such time as all of the Holders are eligible to sell their Warrant Shares
and PIK Shares under Rule 144(k) under the Act. The Company shall utilize Form
S-3 if it qualifies for such use. The Company will furnish to the Holders of
Warrants, Warrant Shares, and PIK Shares registered for sale under the Act (the
"Selling Securities Holders") such numbers of copies of a prospectus, including
a preliminary prospectus, in conformity with the requirements of the Act and
such other related documents as the Selling Securities Holders may reasonably
request in order to effect the sale of the Warrants, Warrant Shares, and PIK
Shares. To effect any offering pursuant to a registration statement under this
Section, the Company shall enter into an agreement containing customary
representations and warranties, and indemnification and contribution provisions,
all for the benefit of Selling Securities Holders, and, in the case of an
Underwritten public offering, an underwriting agreement with an investment
banking firm selected by the Selling Security Holders and reasonably acceptable
to the Company, containing such customary representations and warranties, and
indemnification and contribution provisions

                                       12
<PAGE>

      18.2 "Piggy-Back Registration." If, at any time, the Company proposes to
register any of its securities under the Act (otherwise than pursuant to Section
18.1 or on a Form S-8 if such form cannot be used for registration of the
Warrant, Warrant Shares, or PIK Shares pursuant to its terms), and the
registration statement described in Section 18.1 shall not then be effective
under the Act, the Company shall, as promptly as practicable, give written
notice to the Lender. The Company shall include in such registration statement
the Warrants, Warrant Shares, and PIK Shares proposed to be sold by the Selling
Securities Holders. Notwithstanding the foregoing, if the offering of the
Company's securities is to be made through underwriters, the Company shall not
be required to include the Warrants, Warrant Shares, and PIK Shares if and to
the extent that the managing underwriter reasonably believes in good faith that
such inclusion would materially adversely affect such offering unless the
Selling Securities Holders agree to postpone their sales until 10 days after the
distribution is completed.

      18.3 Costs of Registration. The Company shall pay the cost of the
registration statements filed pursuant to this Agreement, including without
limitation all registration and filing fees, fees and expenses of compliance
with securities or blue sky laws (including counsel's fees and expenses in
connection therewith), printing expenses, messenger and delivery expenses,
internal expenses of the Company, listing fees and expenses, and fees and
expenses of the Company's counsel, independent accountants and other persons
retained or employed by the Company. Selling Securities Holders shall pay any
underwriters discounts applicable to the Warrants, Warrant Shares, and PIK
Shares.

      Section 19. Legends. The Warrants and Warrant Shares issued pursuant to
this Agreement and any PIK Shares that may be issued shall bear an appropriate
legend, conspicuously disclosing the restrictions on exercise and transfer under
Section 7.2 of this Agreement until the same are registered for sale under the
Act. The Company agrees that upon the sale of the Warrants, Warrant Shares, and
PIK Shares pursuant to a registration statement or an exemption, upon the
presentation of the certificates containing such a legend to it's transfer
agent, it will remove such legend. The Company further agrees to remove the
legend at such time as registration under the Act shall no longer be required.

      Section 20. Applicable Law. This Agreement and each Warrant issued
hereunder shall be governed by and construed in accordance with the laws of the
State of California, without giving effect to principles of conflict of laws.

      Section 21. Benefits of this Agreement. Nothing in this Agreement shall be
construed to give to any person or corporation other than the Company, the
warrant agent (if appointed) and the Holders any legal or equitable right,
remedy or claim under this Agreement; but this Agreement shall be for the sole
and exclusive benefit of the Company, the warrant agent and the Holders of the
Warrants.

      Section 22. Counterparts. This Agreement may be executed in any number of
counterparts and each of such counterparts shall for all purposes be deemed to
be an original, and all such counterparts shall together constitute but one and
the same instrument.

                                       13
<PAGE>


      Section 23. Captions. The captions of the Sections and subsections of this
Agreement have been inserted for convenience only and shall have no substantive
effect.

      IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed, all as of the day and year first above written.

                                 BIOTIME, INC.


                                 By: _______________________________________
                                     Name: Paul Segall, Ph.D
                                     Title: Chairman and Chief Executive Officer

Attest:

By: _________________________________
   Name: Judith Segall
   Title: Secretary


                                       14
<PAGE>



                                                                       EXHIBIT A

                                     LENDERS

<TABLE>
<CAPTION>
                                          PRINCIPAL
                                          AMOUNT OF            NUMBER OF
                                          DEBENTURES         WARRANT SHARES
                                         ------------            -------
<S>                                      <C>                 <C>
Alfred D. Kingsley                       $  1,500,000            139,999

Camco Tactical Return Partners, LP       $    500,000             33,333

George Karfunkel                         $    500,000             33,333

Goren Brothers, L.P.                     $    250,000             16,666
</TABLE>



                                       15
<PAGE>

                                                                       EXHIBIT B

      THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, OR UNDER APPLICABLE STATE SECURITIES LAWS. THIS WARRANT MAY NOT BE
EXERCISED, SOLD, PLEDGED, HYPOTHECATED, TRANSFERRED OR ASSIGNED EXCEPT UNDER AN
EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT AND APPLICABLE STATE SECURITIES
LAWS, UNLESS AN EXEMPTION FROM SUCH REGISTRATION IS AVAILABLE.

                VOID AFTER 5:00 P.M. NEW YORK TIME, APRIL 1, 2006


Certificate No.
               ------                                        Warrant to Purchase
                                                       [Insert number of Shares]
                                                          Shares of Common Stock

                                  BIOTIME, INC.
                         COMMON STOCK PURCHASE WARRANTS

      This certifies that, for value received, [Insert name of Holder] or
registered assigns (the "Holder"), is entitled to purchase from BioTime, Inc. a
California corporation (the "Company"), at a purchase price per share [Insert
Warrant Price determined pursuant to Sections 4 and 10 of the Warrant Agreement]
(the "Warrant Price"), the number of its Common Shares, no par value per share
(the "Common Stock"), shown above. The number of shares purchasable upon
exercise of the Common Stock Purchase Warrants (the "Warrants") and the Warrant
Price are subject to adjustment from time to time as set forth in the Warrant
Agreement referred to below. Outstanding Warrants not exercised prior to 5:00
p.m., New York time, on April 1, 2006 shall thereafter be void.

      Subject to restriction specified in the Warrant Agreement, Warrants may be
exercised in whole or in part by presentation of this Warrant Certificate with
the Purchase Form on the reverse side hereof duly executed, which signature
shall be guaranteed by a bank or trust company or a broker or dealer which is a
member of the National Association of Securities Dealers, Inc., and simultaneous
payment of the Warrant Price (or as otherwise set forth in Section 10.5 of the
Warrant Agreement) at the principal office of the Company (or if a warrant agent
is appointed, at the principal office of the warrant agent). Payment of the
Warrant Price shall be made in cash or by certified or bank cashier's check or
by delivery of Debentures in such amount as provided in Section 3 of the Warrant
Agreement. As provided in the Warrant Agreement, the Warrant Price and the
number or kind of shares which may be purchased upon the exercise of the Warrant
evidenced by this Warrant Certificate are, upon the happening of certain events,
subject to modification and adjustment.



                                      A-2
<PAGE>



      The Warrants evidenced by this Warrant Certificate may be redeemed by the
Company, at its election, at any time if (a) a registration statement under
Section 18.1 of the Warrant Agreement or a registration statement under Section
18.2 of the Warrant Agreement that includes Warrants and Warrant Shares is then
effective under the Securities Act of 1933, as amended, and (b) the closing
price of the Common Stock on a national securities exchange (including the
Nasdaq Stock Market National Market System) , or the average bid price as quoted
in Nasdaq Stock Market if the Common Shares are not listed on a national
securities exchange, equals or exceeds 200% of the Warrant Price for any twenty
(20) consecutive trading days ending not more than twenty (20) days prior to the
date of the notice given pursuant to Section 6.2 of the Warrant Agreement. From
and after the date specified by the Company for redemption of the Warrants (the
"Redemption Date"), the Warrants evidenced by this Warrant Certificate shall no
longer be deemed outstanding and all rights of the Holder of this Warrant
Certificate shall cease and terminate, except for the right of the registered
Holder to receive payment of the redemption price of five cents ($0.05) per
Warrant Share upon presentation and surrender of this Warrant Certificate. The
Redemption Date shall abate, and the notice of redemption shall be of no effect,
if the closing price or average bid price of the Common Stock, as applicable
under Section 6.1 of the Warrant Agreement, does not equal or exceed 120% of the
Warrant Price on the Redemption Date and the five trading days immediately
preceding the Redemption Date, but the right Company shall have the right to
redeem the Warrants at a future date if the conditions set forth in Section 6.1
of the Warrant Agreement are subsequently met and a new notice setting a new
Redemption Date is sent to Warrant holders.

      This Warrant Certificate is issued under and in accordance with a Warrant
Agreement dated as of April 9, 2003 between the Company and the persons named as
"Lenders" therein, and is subject to the terms and provisions contained in the
Warrant Agreement, to all of which the Holder of this Warrant Certificate by
acceptance of this Warrant Certificate consents. A copy of the Warrant Agreement
may be obtained by the Holder hereof upon written request to the Company. In the
event that pursuant to Section 14 of the Warrant Agreement a warrant agent is
appointed and a new warrant agreement entered into between the Company and such
warrant agent, then such new warrant agreement shall constitute the Warrant
Agreement for purposes hereof and this Warrant Certificate shall be deemed to
have been issued pursuant to such new warrant agreement.

      Upon any partial exercise of the Warrant evidenced by this Warrant
Certificate, there shall be issued to the Holder hereof a new Warrant
Certificate in respect of the shares of Common Stock as to which the Warrant
evidenced by this Warrant Certificate shall not have been exercised. This
Warrant Certificate may be exchanged at the office of the Company (or the
warrant agent, if appointed) by surrender of this Warrant Certificate properly
endorsed either separately or in combination with one or more other Warrant
Certificates for one or more new Warrant Certificates evidencing the right of
the Holder thereof to purchase the aggregate number of shares as were
purchasable on exercise of the Warrants evidenced by the Warrant Certificate or
Certificates exchanged. No fractional shares will be issued upon the exercise of
any Warrant, but the Company will pay the cash value thereof determined as
provided in the Warrant Agreement. This Warrant Certificate is transferable at
the office of the Company (or the warrant agent, if appointed) in the manner and
subject to the limitations set forth in the Warrant Agreement.

                                      A-3
<PAGE>

      The Holder hereof may be treated by the Company, the warrant agent (if
appointed) and all other persons dealing with this Warrant Certificate as the
absolute owner hereof for any purpose and as the person entitled to exercise the
rights represented hereby, or to the transfer hereof on the books of the
Company, any notice to the contrary notwithstanding, and until such transfer on
such books, the Company (and the warrant agent, if appointed) may treat the
Holder hereof as the owner for all purposes.

      Neither the Warrant nor this Warrant Certificate entitles any Holder to
any of the rights of a stockholder of the Company.

      [This Warrant Certificate shall not be valid or obligatory for any purpose
until it shall have been countersigned by the warrant agent.]*

DATED:

                                                     BIOTIME, INC.


(Seal)                                               By:________________________

                                                     Title: ____________________

Attest:____________________


[COUNTERSIGNED:


WARRANT AGENT

By:_________________________]*
     Authorized Signature

___________________________

*     To be part of the Warrant only after the appointment of a warrant agent
      pursuant to Section 14 of the Warrant Agreement.




                                      A-4
<PAGE>




                                  PURCHASE FORM

                    (To be executed upon exercise of Warrant)



To BioTime, Inc.:

      The undersigned hereby irrevocably elects to exercise the right of
purchase represented by the within Warrant Certificate for, and to purchase
thereunder, _______ shares of Common Stock, as provided for therein, and tenders
herewith payment of the Warrant Price in full in the form of cash or a certified
or bank cashier's check or outstanding Series 2001-A Debentures in the amount of
$______________.

      Please issue a certificate or certificates for such shares of Common Stock
in the name of, and pay any cash for any fractional share to:

------------------------------------
(Please Print Name)

------------------------------------
(Please Print Address)

------------------------------------
(Social Security Number or
Other Taxpayer Identification Number)

------------------------------------
 (Signature)

NOTE: The above signature should correspond exactly with the name on the face of
      this Warrant Certificate or with the name of the assignee appearing in the
      assignment form below.

And, if said number of shares shall not be all the shares purchasable under the
within Warrant Certificate, a new Warrant Certificate is to be issued in the
name of said undersigned for the balance remaining of the share purchasable
thereunder less any fraction of a share paid in cash.



                                      A-5