NEITHER THIS  DEBENTURE,  NOR THE SHARES  ISSUABLE UPON  CONVERSION OF THIS
DEBENTURE HAVE BEEN  REGISTERED  WITH THE UNITED STATES  SECURITIES AND EXCHANGE
COMMISSION OR THE  SECURITIES  COMMISSION OF ANY STATE  PURSUANT TO AN EXEMPTION
FROM  REGISTRATION  UNDER  REGULATION S PROMULGATED  UNDER THE SECURITIES ACT OF
1933, AS AMENDED (THE 'ACT').  THIS  DEBENTURE  SHALL NOT CONSTITUTE AN OFFER TO
SELL NOR A SOLICITATION OF AN OFFER TO BUY THE SECURITIES IN ANY JURISDICTION IN
WHICH  SUCH  OFFER  OR  SOLICITATION  WOULD  BE  UNLAWFUL.  THE  SECURITIES  ARE
'RESTRICTED' AND MAY NOT BE RESOLD OR TRANSFERRED  EXCEPT AS PERMITTED UNDER THE
ACT PURSUANT TO AN  EFFECTIVE  REGISTRATION  STATEMENT OR AN EXEMPTION  FROM THE
REGISTRATION REQUIREMENTS OF SUCH ACT

     NEITHER THIS  DEBENTURE,  NOR THE SHARES  ISSUABLE UPON  CONVERSION OF THIS
DEBENTURE  MAY BE OFFERED OR SOLD IN THE UNITED  STATES OR TO U.S.  PERSONS  (AS
SUCH TERM IS DEFINED  IN  REGULATION  S  PROMULGATED  UNDER THE ACT)  UNLESS THE
SECURITIES  ARE REGISTERED  UNDER THE ACT OR PURSUANT TO AN AVAILABLE  EXEMPTION
FROM THE REGISTRATION REQUIREMENTS OF THE ACT.

     THIS DEBENTURE  DOES NOT CONSTITUTE AN OFFER TO SELL, OR A SOLICITATION  OF
AN OFFER TO BUY,  ANY OF THE  SECURITIES  OFFERED  HEREBY  BY ANY  PERSON IN ANY
JURISDICTION IN WHICH IT IS UNLAWFUL FOR SUCH PERSON TO MAKE SUCH AN OFFERING OR
SOLICITATION. IN MAKING AN INVESTMENT DECISION, INVESTORS MUST RELY ON THEIR OWN
EXAMINATION  OF THE COMPANY AND THE TERMS OF THE OFFERING,  INCLUDING THE MERITS
AND THE  RISKS  INVOLVED.  THESE  SECURITIES  HAVE NOT BEEN  RECOMMENDED  BY ANY
FEDERAL OR STATE SECURITIES COMMISSION OR REGULATORY AUTHORITY. FURTHERMORE, THE
FOREGOING AUTHORITIES HAVE NOT CONFIRMED THE ACCURACY OR DETERMINED THE ADEQUACY
OF THIS DOCUMENT. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

No.                                                                 $       U.S.
   ----------                                                        -------

                              CELGENE CORPORATION

                   8% CONVERTIBLE DEBENTURE DUE JULY 31, 1997

     THIS DEBENTURE is one of a duly  authorized  issue of Debentures of CELGENE
CORPORATION,  a corporation  duly  organized and existing  under the laws of the
State of Delaware (the 'Company'),  designated as its 8% Convertible  Debentures
Due  July  31,  1997,  in an  aggregate  principal  amount  not  exceeding  U.S.
$12,000,000

     FOR  VALUE  RECEIVED,  the  Company  promises  to  pay to  __________,  the
registered    holder   hereof   (the    'Holder'),    the   principal   sum   of
___________________  ($_________  U.S.),  on or  prior  to July  31,  1997  (the
'Maturity Date') and to pay (continued on reverse)

IN WITNESS  WHEREOF,  the Company has caused this instrument to be duly executed
by an officer thereunto duly authorized.

                              CELGENE CORPORATION


Dated: July 1995              By:___________________________________
                                  Dr. Sol J. Barer,
                                  President and Chief
                                  Operating Officer







(page 2 of  4 of Celgene Corporation Convertible Debenture due July 31, 1997)

interest on the  principal sum  outstanding  from time to time in arrears on the
Maturity  Date,  at the rate of 8% per annum  accruing  from the date of initial
issuance.  Accrual of interest shall commence on the first business day to occur
after the date hereof until  payment in full of the  principal sum has been made
or duly  provided for. The interest so payable will be paid on the Maturity Date
to the  person  in  whose  name  this  Debenture  (or  one or  more  predecessor
Debentures) is registered on the records of the Company  regarding  registration
and transfers of the Debentures (the 'Debenture Register') on the first business
day prior to the Maturity Date: provided, however, that the Company's obligation
to a transferee of this Debenture  arises only if such  transfer,  sale or other
disposition  is  made  in  accordance  with  the  terms  and  conditions  of the
Regulation  S  Subscription  Agreement  executed  by the  original  Holder  or a
subsequent  transferee.  All accrued and unpaid  interest shall bear interest at
the same rate of 8% per annum from the Maturity  Date until the date of payment.
The  principal  of, and interest on, this  Debenture are payable in such coin or
currency  of the  United  States of  America  as at the time of payment is legal
tender for  payment of public and  private  debts,  at the address of the Holder
last appearing on the Debenture Register of the Company as designated in writing
by the Holder from time to time.  The  Debenture  Register  shall  represent the
record  of  ownership  and  right to  receive  principal  and  interest  on this
Debenture. Interest and principal shall be payable only to the registered Holder
as  reflected  in the  Debenture  Register.  A transfer  of the right to receive
principal and interest under this Debenture shall be  transferable  only through
an  appropriate  entry  in  the  Debenture  Register  as  provided  herein.  The
forwarding of such payment shall constitute a payment of interest  hereunder and
shall  satisfy and  discharge  the  liability for principal and interest on this
Debenture to the extent of the sum represented by such payment.

     This Debenture is subject to the following additional provisions:

     1. The Debentures  are issuable in  denominations  of One Hundred  Thousand
Dollars  ($100,000  U.S.)  and  integral  multiples  of Fifty  Thousand  Dollars
($50,000 U.S.) in excess thereof.  The Debentures are  exchangeable for an equal
aggregate principal amount of Debentures of different authorized  denominations,
as requested by the Holders  surrendering  the same but shall not be issuable in
denominations  less than integral  multiples of Fifty Thousand  Dollars ($50,000
U.S.).  No service  charge  will be made for such  registration  of  transfer or
exchange.

     2. The Company shall be entitled to withhold from all payments of principal
of, and interest on, this  Debenture any amounts  required to be withheld  under
the  applicable  provisions  of the  United  States  income  tax  laws or  other
applicable  laws at the time of such  payments.  The Holder  shall pay any other
taxes, charges, or levies in connection with the issuance or transfer thereof.

     3. This Debenture has been issued subject to investment  representations of
the  original  purchaser  hereof and may be  transferred  or  exchanged  only in
compliance  with the Securities  Act of 1933, as amended (the 'Act'),  including
Regulation  S  promulgated  under  the Act.  Any  Holder of this  Debenture,  by
acceptance  hereof,  agrees to the  representations,  warranties  and  covenants
herein.  Prior to due presentment to the Company for transfer of this Debenture,
the Company and any agent of the Company may treat the person in whose name this
Debenture is duly  registered on the Company's  Debenture  Register as the owner
hereof for the purpose of receiving payment as herein provided and for all other
purposes,  whether or not this Debenture be overdue, and neither the Company nor
any such agent shall be affected by notice to the contrary.

     4. The Holder of this  Debenture  is entitled,  at its option,  at any time
commencing  on July 29, 1995 until  September  11, 1995 to convert the principal
amount of this Debenture, in whole but not in part, into shares of Common Stock,
par value $.01 per share (the  'Common  Stock') of the  Company at a  conversion
price (the 'Fixed  Conversion  Price')  for each share of Common  Stock equal to
100% of the Closing Bid Price, as defined, on July 28, 1995 and is entitled,  at
its option at any time  commencing  on  September  12,  1995 until July 30, 1997
(which is the last  business day prior to the  Maturity  Date hereof) to convert
the principal amount of this Debenture, in whole but not in part, into shares of
Common Stock of the Company at a conversion price ('Variable  Conversion Price')
for each share of Common  Stock  equal to the lesser of (a)  Eight-five  percent
(85%) of the Market Price (as defined) of the  Company's  Common  Stock,  or (b)
100% of the Closing Bid Price,  as defined,  on July 28,  1995.  For purposes of
this  Section 4, the  'Closing Bid Price' of the Common Stock for each day shall
be the closing bid price of the Common  Stock on such day as reported on the New
York Stock  Exchange  composite  tape,  or, if the Common Stock is not listed or
admitted for trading on such  Exchange,  on the  principal  national  securities
exchange on which is the Common Stock is listed or admitted  for trading,  or if
not listed or admitted  for trading on any  national  securities  exchange,  the
closing bid price of the Common Stock as reported by the National Association of
Securities Dealers Automated  Quotation System ('NASDAQ') National Market System
(or, if not so reported, the closing price) or, if not admitted for quotation on
the NASDAQ National Market System, the average of the high bid and the low asked
prices as recorded by the  National  Association  of  Securities  Dealers,  Inc.
through  NASDAQ,  or, if the Common Stock is not traded in the  over-the-counter
market,  the fair  market  value of one  share  of  Common  Stock on such day as
determined  in good faith by the Board of  Directors  (which  decision  shall be
conclusive).  For  purposes of this  Section 4,  'Market  Price'  shall mean the
average of the Closing Bid Price for the five  trading days prior to the Date of
Conversion  (as  herein  defined).  Such  conversion  shall  be  effectuated  by
surrendering  the  Debentures  to be  converted  by  overnight  courier  to  the
Company's  registrar and transfer  agent,  American  Stock  Transfer & Trust Co.
('Transfer  Agent'),  with the form of  conversion  notice  attached  hereto  as
Exhibit A (with an advance copy of the  Debenture and the  conversion  notice to
the Transfer Agent and the Company by facsimile), executed by the Holder of this
Debenture  evidencing  such Holder's  intention to convert this  Debenture,  and
accompanied,  in the event the Holder  desires to register  the shares of Common
Stock in a name other  than that of Holder,  by proper  assignment  hereof.  The
Company and the  Transfer  Agent shall make a  reasonable  effort to deliver the
converted  shares to the Holder within three  business days from date of receipt
of the conversion  notice and the original of this  Debenture.  In the event the
Holder  converts  the  Debenture  at the  Fixed  Conversion  Price  or  Variable
Conversion  Price, the accrued interest shall be payable to the Holder in shares
of Common Stock  (unless such  Debenture is redeemed for cash under the terms of
Section 5 herein),  and the interest and number of shares issued upon conversion
shall be  calculated  as  follows:

     Number of shares issued upon conversion = (Principal + Interest)/Conversion
         Price,  where 

           Principal  = The  principal amount of the  Debenture to be converted,

           Interest = Principal x (N/365) x .08, where N = the number of days 
           from July 28, 1995 to the date of conversion, and 

           Conversion Price = Either the Fixed Conversion Price or the Variable
           Conversion Price, as defined in this paragraph 4 herein, whichever is
           applicable at the time of such conversion.

                               (continued on attached)



(page 3 of 4 of Celgene Corporation Convertible Debenture due July 31, 1997)

In all cases the conversion of this Debenture in full shall represent payment of
all  interest and  principal  payable to the Holder  hereunder.  No fractions of
shares or scrip  representing  fractions of shares will be issued on conversion,
but the  number of shares  issuable  shall be rounded  up to the  nearest  whole
share.  The  date  on  which  notice  of  conversion  is  given  (the  'Date  of
Conversion')  shall  be  deemed  to be the  date set  forth  in such  notice  of
conversion if the original of this  Debenture is received by the Transfer  Agent
within five business days  thereafter.  If the original of this Debenture is not
received  by the  Transfer  Agent  within five  business  days after the Date of
Conversion, the notice of conversion shall become null and void. In the event of
any stock split,  stock dividend payable in securities of the Company,  or other
reclassification  of the Common Stock,  the conversion  price shall be equitably
adjusted so that the Holder shall receive, in exchange for the conversion price,
such  securities or other property which it would have received had it converted
this  Debenture  immediately  prior  to such  stock  split,  dividend  or  other
reclassification. No service charge will be made for any such conversion.

     5. The Company  shall have the right to redeem this  Debenture  for cash by
giving notice (the 'Redemption Notice') to the Holder by facsimile,  original to
follow by two-day  courier,  within  one  business  day from the date  facsimile
notice of conversion is received by the Company.  The redemption  price shall be
paid to Holder within seven  calendar  days after such  facsimile has been given
except in the event the Common  Stock  price is below  $5.00,  in which case the
redemption  price  shall be paid to Holder  within 21  calendar  days after such
facsimile notice has been given.  The redemption price (the 'Redemption  Price')
shall be the greater of a) the amount  calculated by multiplying  the sum of the
Principal and accrued Interest of this Debenture,  as those terms are defined in
paragraph 4 above,  by a fraction,  the  numerator of which shall be the Closing
Bid Price on the proposed Date of Conversion, and the denominator of which shall
be the lesser of the  conversion  prices  described  in  clauses  (a) and (b) of
Section 4 above,  and b) 115% of the  Principal  and  accrued  Interest  of this
Debenture.  After receipt of the Redemption  Notice,  all rights with respect to
this Debenture,  including,  without limitation, the conversion rights contained
herein  (notwithstanding  the  furnishing  by the  holder  hereof of a notice of
conversion to the Company), shall forthwith terminate,  except only the right of
the holder to receive the Redemption Price.

     6. The Company is entitled,  at its option,  any time commencing on October
15, 1995 until July 30, 1996 to require the Holder to convert the  Principal and
accrued  Interest of this  Debenture,  as those terms are defined in paragraph 4
above, into shares of Common Stock of the Company at a conversion price for each
share of Common  Stock equal to the lesser of a) 75% of the Closing Bid Price on
the date the Company  provides  notice of conversion  and b) 100% of the Closing
Bid Price on July 28,  1995.  The Company is entitled,  at its option,  any time
commencing on July 31, 1996 until July 30, 1997 to require the Holder to convert
the Principal and accrued Interest of this Debenture, as those terms are defined
in paragraph 4 above, into shares of Common Stock of the Company at a conversion
price  for each  share of  Common  Stock  equal to the  lesser  of (a) or (b) of
Section 4 above.  In either  case,  the Company  shall  notify the Holder of the
Company's  intent to force  conversion  by giving  written  notice  ('Notice  of
Mandatory Conversion') to the Holder by facsimile, original to follow by two-day
courier,  before  midnight,  New York City time,  on the date of such  mandatory
conversion. The Company is not entitled to require conversion under this Section
6 if the  Company  makes  any  planned  press  release  either  a) on the day it
provides  such Notice of Mandatory  Conversion  to the Holder or b) prior to the
close of trading on the following business day.

     7. Except as expressly  provided  herein,  no  provision of this  Debenture
shall alter or impair the  obligation  of the  Company,  which is  absolute  and
unconditional,  to pay the principal of, and interest on, this  Debenture at the
time,  place,  and rate, and in the coin or currency,  herein  prescribed.  This
Debenture and all other  Debentures now or hereafter issued of similar terms are
direct  obligations  of the Company.  This  Debenture  ranks pari passu with all
other Debentures now or hereafter issued under the terms set forth herein.

     8. Except as provided by applicable  law, no recourse  shall be had for the
payment of the  principal  of, or the  interest on, this  Debenture,  or for any
claim based hereon,  or otherwise in respect hereof,  against any  incorporator,
shareholder,  officer or director,  as such, past,  present,  or future,  of the
Company or of any successor corporation,  whether by virtue of any constitution,
statute or rule of law, or by the  enforcement  of any  assessment or penalty or
otherwise, all such liability being, by the acceptance hereof and as part of the
consideration for the issue hereof, expressly waived and released.

     9. After this  Debenture  shall have been  surrendered  for  conversion  as
herein  provided  or notice of  conversion  shall have been given by the Company
pursuant  to Section 6 herein,  this  Debenture  shall no longer be deemed to be
outstanding  and all rights with respect to this Debenture,  including,  without
limitation,  the right to recei ve  interest  hereon and the  principal  hereof,
shall forthwith terminate as of the Date of Conversion, except only the right of
the holder hereof to receive shares of Common Stock in exchange herefor.

     10. This Debenture shall not entitle the holder hereof to any of the rights
of a stockholder  of the Company,  including  without  limitation,  the right to
vote, to receive dividends and other distributions, or to receive any notice of,
or to attend, meetings of stockholders or any other proceedings of the Company.

     11. If this Debenture shall be mutilated,  lost,  stolen or destroyed,  the
Company shall  execute and deliver,  in exchange and  substitution  for and upon
cancellation of a mutilated  Debenture,  or in lieu of or in substitution  for a
lost, stolen or destroyed Debenture, a new Debenture for the principal amount of
this Debenture so mutilated,  lost, stolen or destroyed but only upon receipt of
evidence  of such  loss,  theft or  destruction  of such  Debenture,  and of the
ownership thereof, and indemnity,  if requested,  all reasonably satisfactory to
the Company.

     12. Any Holder of this Debenture,  by acceptance  hereof,  agrees that such
Holder will not offer, sell or otherwise dispose of this Debenture or the shares
of Common Stock issuable upon exercise thereof except under  circumstances which
will not result in a violation of the Act,  including  Regulation S  promulgated
under the Act, or any applicable  state Blue Sky law or similar laws relating to
the sale of  securities  and the holder  agrees to provide the Company with such
documentation  as the Company shall deem necessary in accordance  with Section 4
of the  Regulation S  subscription  agreement  executed by the  original  holder
hereof to demonstrate that

                            (continued on attached)


(page 4 of 4 of Celgene Corporation Convertible Debenture due July 31, 1997)

such offer, sale or disposition  complied with applicable  securities laws. This
provision shall similarly apply to subsequent transfers of this Debenture.

     13.This Debenture shall be governed by and construed in accordance with the
laws of the State of Delaware, without giving effect to conflicts of laws.

     14.For purposes hereof, the term 'business day' shall mean any day on which
banks  are  generally  open  for  business  in the  State of  Delaware,  USA and
excluding any Saturday and Sunday.

     15. In the event of a merger,  reorganization,  recapitalization or similar
event of or with  respect to the Company (a  'Corporate  Change')  (other than a
Corporate Change in which all or substantially all of the consideration received
by the holders of the Company's  equity  securities  upon such Corporate  Change
consists of cash or assets other than securities  issued by the acquiring entity
or any  affiliate  thereof),  this  Debenture  shall be assumed by the acquiring
entity and thereafter  this Debenture  shall be convertible  into such class and
type of securities  as the Holder would have  received had the Holder  converted
this Debenture immediately prior to such Corporate Change.

     16. Any notice or other  communication  required or  permitted  to be given
hereunder shall be given as provided  herein or delivered  against receipt if to
(i) the Company at, 7 Powder Horn Drive, Warren, New Jersey 07059,  Telecopy No.
(908) 805-3931 and (ii) the holder of this Debenture, to such holder at its last
address as shown on the  Debenture  Register  (or to such  other  address as the
party shall have furnished in writing in accordance  with the provisions of this
Section 16). Any notice or other communication mail shall be deemed given at the
time of receipt thereof.

     17.  Any  waiver by the  Company  or the  holder  hereof of a breach of any
provision of this Debenture  shall not operate as or be construed to be a waiver
of any other breach of such provision or of any breach of any other provision of
this  Debenture.  The failure of the Company or the holder hereof to insist upon
strict  adherence to any term of this Debenture on one or more  occasions  shall
not be  considered  a waiver or deprive  that party of the right  thereafter  to
insist upon strict  adherence to that term or any other term of this  Debenture.
Any waiver must be in writing.

     18.  If  any   provision  of  this   Debenture   is  invalid,   illegal  or
unenforceable,  the balance of this Debenture shall remain in effect, and if any
provision is inapplicable to any person or circumstance,  it shall  nevertheless
remain applicable to all other persons and circumstances.





                                   EXHIBIT A

                              NOTICE OF CONVERSION

                    (To be Executed by the Registered Holder
                    in order to Convert the Debenture)Holder

The undersigned hereby irrevocably elects to convert the above Debenture No.
___________ into shares of Common Stock, par value $.01 per share (the 'Common
Stock'), of Celgene Corporation (the 'Company') according to the conditions
hereof, as of the date written below. If shares are to be issued in the name of
a person other than undersigned, the undersigned will pay all transfer taxes
payable with respect thereto and is delivering herewith such certificates and
opinions as reasonably requested by the Company. No fee will be charged to the
Holder for any conversion, except for transfer taxes, if any.

If this Debenture is being converted during the Restricted Period (as that term
is defined in the subscription agreement executed by the original purchaser of
this Debenture), the undersigned represents that it is not a U.S. Person as
defined in Regulation S promulgated under the United States Securities Act of
1933, as amended (the 'Act') and is not converting the Debenture on behalf of
any U.S. Person. The undersigned also represents and warrants that all offers
and sales by the undersigned of the shares of Common Stock issuable to the
undersigned upon conversion of the Debenture shall be made in compliance with
Regulation S, pursuant to registration of the Common Stock under the Act or
pursuant to an exemption from registration under the Act.


Conversion calculations:                        --------------------------------
                                                 Date of Conversion


                                                --------------------------------
                                                 Applicable Conversion Price


                                                --------------------------------
                                                 Signature


                                                --------------------------------
                                                 Name


                                                 Address
                                                --------------------------------
                                                --------------------------------

* The original Debenture and Notice of Conversion must be received by the
Company's Transfer Agent before any shares of Common Stock will be issued. If
the original of this Debenture is not received by the Transfer Agent (or such
other person as the Company may specify) within five business days after the
date of conversion specified above, this notice of conversion shall become null
and void.