Document:

NON-RECOURSE SECURED PROMISSORY NOTE
          ------------------------------------

$277,805.07                                   June 11, 1999

        FOR VALUE RECEIVED, Bruce C. Galton (the "Maker")
hereby promises to pay to the order of Cistron Biotechnology,
Inc., a Delaware corporation ("Cistron"), at Cistron's principal
offices at 10 Bloomfield Avenue, Pine Brook, New Jersey 07058,
or such other address as Cistron shall have given to the maker,
the principal sum of Two hundred Seventy Seven Thousand Eight
Hundred and Five ($277,805.07) Dollars and Seven Cents on the
earliest of June 10, 2002, the merger or sale of Cistron, or the
liquidation or dissolution of Cistron,

        Payments shall be made in such currency of the United
States as at the time of payment shall be legal tender for the
payment of public and private debts.

        This Note evidences the Loan made by Cistron under the
Loan and Pledge Agreement dated the date hereof (the
"Agreement") between Cistron and the Maker providing, among
other things, for the securing of the Note by a pledge of the
Shares, for the prepayment of this Note and for the acceleration
of the maturity of this Note following an Event of Default, all
on the terms set forth in the Agreement.

        This Note may be prepaid, in whole or in part, at any
time and from time to time without premium.  This Note shall be
paid without deduction by reason of any set-off, defense or
counterclaim of the Maker.

        Upon any sale of the Shares, this Note shall become
due and payable as set forth in the Agreement.  In addition,
upon the occurrence of an Event of Default (as defined in the
Agreement), this Note shall become due and payable as set forth
in the Agreement.

        The Maker does not assume any personal liability or
responsibility for the failure to pay the principal amount of
this Note.  The sole remedy available upon such failure shall be to

<PAGE> 2

proceed against the Collateral in accordance with the terms
of the Agreement.

        The maker hereby forever waives presentment, demand,
presentment for payment, protest, notice of protest, notice of
dishonor of this Note and all other demands and notices in
connection with the delivery, acceptance, performance and
enforcement of this Note.

        This Note shall be governed by and construed in
accordance with the laws of the State of New Jersey and shall be
binding upon the heirs or legal representatives of the Maker and
shall inure to the benefit of the successors and assigns of
Cistron.

                                	/s/BRUCE C. GALTON
                                 ------------------
                             				   BRUCE C. GALTONEXHIBIT 4.1

                                 ---------------

                                Warrant Agreement

                         Dated as of September 13, 1995

                                 ---------------

<PAGE>

                  WARRANT AGREEMENT, dated as of September 13, 1995, between
Biotime, Inc., a California corporation (the "Company"), and Greenbelt Corp., a
Delaware corporation (the "Financial Advisor").

                  The Company proposes to issue Common Share Purchase  Warrants,
as  hereinafter  described (the  "Warrants"),  to purchase up to an aggregate of
300,000  shares 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"),  in  connection  with the  agreement,  dated
September  13, 1995 (the  "Consulting  Agreement"),  between the Company and the
Financial  Advisor;  each Warrant  entitling the holder  thereof to purchase one
share of Common Stock.

                  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 the registered owners of the Warrants
(the "Holders"), the Company and the Financial Advisor hereby agree as follows:

                  SECTION  1.   Issuance   of   Warrants;   Term  of   Warrants.
Concurrently  with  the  execution  and  delivery  of  this  Agreement  and  the
Consulting  Agreement,  the Company is issuing and  delivering  to the Financial
Advisor  Warrants to purchase  100,000 Warrant  Shares,  which Warrants shall be
represented  by a  certificate  in  substantially  the form of Exhibit A hereto.
Subject to the terms of this Agreement, a Holder of any of such 100,000 Warrants
shall have the right,  which may be exercised  at any time after 9:00 a.m.,  New
York time, on October 15, 1996, and prior to 5:00 p.m., New York Time on October
15, 2000 (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 100,000 Warrants.  The Company
will  issue  and  deliver  additional  Warrants  on such  dates  and  with  such
Expiration  Dates  as  indicated  below,  which  additional  Warrants  shall  be
represented  by  certificates  substantially  in the  form of  Exhibit  A hereto
delivered on the applicable dates of issuance:

                         Additional                               Expiration
Date of Issuance         Warrants                                    Date
----------------         ----------                              --------------
October 15, 1995          25,000                               October 15, 2000
January 15, 1996          25,000                               January 15, 2001
April 15, 1996            25,000                               April 15, 2001
July 15, 1996             25,000                               July 15, 2001
October 15, 1996          25,000                               October 15, 2001

                                        1

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January 15, 1997         25,000                                January 15, 2002
April 15, 1997           25,000                                  April 15, 2002
July 15, 1997            25,000                                   July 15, 2002

; provided,  however,  in the event that the Consulting  Agreement is terminated
prior to July 15,  1997,  the Company  shall issue and deliver to the  Financial
Advisor, as of the date of such termination, the 25,000 additional Warrants that
would  otherwise have been issuable on the next  succeeding date of issuance set
forth above and,  following such issuance and delivery,  no additional  Warrants
shall be issued or delivered hereunder.

Subject  to the  terms of this  Agreement,  a Holder  of any of such  additional
Warrants  shall have the right,  which may be  exercised  at any time after 9:00
a.m.,  New York time,  on the later of (a)  October 15, 1996 and (b) the date of
issuance,  and prior to 5:00 p.m.,  New York time on the  applicable  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 additional Warrants.

          SECTION 2.  Transferability and Form of Warrant.
                      -----------------------------------

                  2.1 Registration.  The Warrants shall be numbered and shall be
registered  on the books of the Company  (the  "Warrant  Register")  as they are
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  Warrants  which  are  registered  or  to be
registered in the name of a fiduciary or the nominee of a 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.  The Warrants
shall initially be registered in the name of the Financial Advisor.

                  2.2  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  and the
Holder shall have  delivered  an opinion of counsel  addressed to the Company to
such effect; provided, that such opinion shall be in form and substance and from
counsel  reasonably  satisfactory to the Company.  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

                                        2

<PAGE>

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.

                  2.3  Transfer.  Subject to Section 2.2, 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.

                  2.4  Form  of  Warrant.  The  text of the  Warrant  and of the
Purchase Form shall be  substantially as set forth in Exhibit A 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
Executive or Senior Vice Presidents, under its corporate seal reproduced thereon
attested by its  Secretary or  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.

                  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 issuance,  division, transfer, exchange
or exercise of Warrants,  the Warrants issued after the date of such appointment
shall be dated as of the date of  countersignature  thereof by the Warrant Agent
either  upon  initial  issuance  or 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.

                  SECTION 3.  Countersignature of Warrants.  In the event that
                              ----------------------------
the Company shall appoint a Warrant Agent to act on its behalf in connection
with the issuance, division, transfer,

                                        3

<PAGE>

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  Warrants  entitling  the Holders  thereof to purchase not more than
300,000 Warrant Shares (subject to adjustment pursuant to Section 10 hereof) and
shall countersign and deliver Warrants as otherwise provided in this Agreement.

                  SECTION 4.  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.

                                        4

<PAGE>

          SECTION 5.  Exercise of Warrants; Listing.
                      -----------------------------

                  5.1  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 Sections 9 and 10 hereof) 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  9  herein)  shall  be  made in cash or by
certified or bank cashier's check.

                  Subject to Section 6 hereof, upon the surrender of the Warrant
and payment of the Warrant Price as aforesaid, the Company (or if appointed, the
Warrant  Agent)  shall  cause to be issued  and  delivered  with all  reasonable
dispatch 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 11 hereof,  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 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  and  Section 3  hereof,  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.

                  5.2 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 6.  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;

                                        5

<PAGE>

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 7. 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 8.  Reservation of Warrant Shares; Purchase
                              ----------------------------------------
                              and Cancellation of Warrants.
                              -----------------------------
                  8.1 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 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 11 hereof.
The  Company  will  furnish  such  Transfer  Agent  a  copy  of all  notices  of
adjustments  and  certificates  related  thereto,  transmitted  to  each  Holder
pursuant to subsection 10.3 hereof.

                  8.2  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.

                  8.3  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

                                        6

<PAGE>

appointed)  shall cancel any Warrant  surrendered  for  exchange,  substitution,
transfer or exercise in whole or in part.

                  SECTION 9. Warrant Price.  Subject to any adjustments required
by Section  10  hereof,  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 a price which shall be the greater of (a) the average
of the last sale prices per share of Common  Stock,  as reported on the National
Association of Securities Dealers,  Inc. Automated Quotations ("NASDAQ") System,
on each  trading day during the three month period prior to the date of issuance
of the  Warrants  multiplied  by 150%,  and (b) six dollars  ($6.00);  provided,
however,  that the Warrant Price of the Warrants issued as of September 13, 1995
is six dollars ($6.00) and, provided,  further,  in the event that the last sale
prices of the Common Stock for the period  indicated in clause (a) above are not
reported on NASDAQ,  clause (a) shall be deemed to refer to the  average  market
price of the Common Stock during such period,  as  reasonable  determined by the
Board  of  Directors  of the  Company  on the  basis of such  quotations  as are
available, multiplied by 150%.

                  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  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

                                        7

<PAGE>

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
Financial  Advisor,  an  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,  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 NASDAQ or any  comparable
system. If the

                                        8

<PAGE>

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 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.

                  (h) For the purpose of this subsection  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 5 and
subsections  10.2 through 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

                                        9

<PAGE>

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
                        ---------------------------
subsection 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 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

                                       10

<PAGE>

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 subsection 10.5 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.  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 11,
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 subsection 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  12. 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

                                       11

<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 (a) give  notice in writing of such event as provided in Section 14 hereof
and (b) if the Warrants have been  registered  pursuant to the Securities Act of
1933, 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 13.  Appointment of Warrant Agent. At such time as the
Company shall  register  Warrants  under the Securities Act of 1933, 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,  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 14. 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.  Each party hereto 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.

                  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.

                                       12

<PAGE>

                  SECTION 15. 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  Financial  Advisor  shall bind and inure to the
benefit of their respective successors and permitted assigns hereunder.

                  SECTION  16.  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 17.  Legends.  The  Warrants  issued  pursuant to this
Agreement  shall  bear  an  appropriate  legend,  conspicuously  disclosing  the
restrictions on exercise and transfer under Section 2.2 of this Agreement.

                  SECTION 18.  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  19.  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 20.  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.

                  SECTION 21.  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:  s/Paul Segall

   Name: Paul Segall, Ph.D
   Title: President and Chief Executive Officer

                                       13

<PAGE>

Attest:

By:       s/Judith Segall

          Name: Judith Segall
          Title: Secretary

GREENBELT CORP.

By:       s/Alfred D.  Kingsley
          Name: Alfred D. Kingsley
          Title: President

Attest:

By:       s/Gary K.  Duberstein
          Name: Gary K. Duberstein
          Title: Vice President

                                       14

<PAGE>

                                                                      EXHIBIT A

                  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 AND THE
HOLDER SHALL HAVE  DELIVERED  AN OPINION OF COUNSEL  ADDRESSED TO THE COMPANY TO
SUCH EFFECT; PROVIDED, THAT SUCH OPINION SHALL BE IN FORM AND SUBSTANCE AND FROM
COUNSEL REASONABLY SATISFACTORY TO THE COMPANY.

VOID AFTER 5:00 P.M. NEW YORK TIME, [INSERT EXPIRATION DATE]

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

Shares of Common Stock

                                  BIOTIME, INC.
                         COMMON SHARE 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 any time after 9:00
A.M., New York time, on [Insert Date of Allowed  Exercise  pursuant to Section 1
of the  Warrant  Agreement  referred  to  below] at a  purchase  price per share
[Insert  Warrant Price  determined  pursuant to Sections 9 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 Share  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 [Insert  Expiration  Date pursuant to Section 1 of
the Warrant Agreement] 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 such price shall be made in cash or by certified

                                       15

<PAGE>

or bank cashier's check. 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.

                  This Warrant  Certificate  is issued  under and in  accordance
with a Warrant  Agreement dated as of September 13, 1995 between the Company and
Greenbelt  Corp.  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 13 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.

                  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:

                                       16

<PAGE>

                  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 13 of the Warrant Agreement.

                                       17

<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 purchase price in full in the form of cash or a
certified or bank cashier's check 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 INSERT SOCIAL SECURITY                    NAME
OR OTHER IDENTIFYING NUMBER                     (Please Print Name &
OF ASSIGNEE                                      Address)

___________________________ Address

___________________________ 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.

                                       18

<PAGE>

                                   ASSIGNMENT

          (To be executed only upon assignment of Warrant Certificate)

                  For value received,  _____________  hereby sells,  assigns and
transfers unto _______________ the within Warrant Certificate, together with all
right, title and interest therein,  and does hereby  irrevocably  constitute and
appoint _________________  attorney, to transfer said Warrant Certificate on the
books of the  within-named  Company,  with  full  power of  substitution  in the
premises.

Dated:___________________       ____________________________

          NOTE:     The above signature should correspond exactly with the name
                    on the face of this Warrant Certificate.

                                       19

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