EXHIBIT 10.1


                                    SUBLEASE
                                    --------

This SUBLEASE (the "Sublease") is dated as of the 23rd day of May, 2002 by and
between HALE AND DORR LLP, a Massachusetts limited liability partnership having
a principal place of business at 60 State Street, Boston, MA 02109
("Sublandlord"), and CYTOGEN CORPORATION, a Delaware corporation having a
principal place of business at 600 College Road East, CN 5308, Princeton, NJ
08540 ("Subtenant").

                                 R E C I T A L S
                                 ---------------

WHEREAS, pursuant to that certain Lease dated as of August 19, 1998 by and
between 650 COLLEGE ROAD ASSOCIATES, L.P. ("Prime Landlord"), as landlord, and
Buchanan Ingersoll Professional Corporation ("BIPC"), as tenant, as amended by
Amendments Number One and Two to Lease Agreement dated as of, respectively, May
23, 2000 and December 1, 2000 (collectively, the "Prime Lease"), a copy of which
Lease and Amendments are attached hereto as Exhibit A, BIPC leased from Prime
Landlord certain premises (the "Original Premises") located on the third and
fourth floors in the building at 650 College Road East, Princeton, NJ 08540 (the
"Building"), which Original Premises contain approximately 68,437 rentable
square feet of space, as more fully described in the Prime Lease; and

WHEREAS, the Prime Lease has been assigned to and assumed by Sublandlord by
Assignment and Assumption Agreement dated February 15, 2001; and

WHEREAS, Subtenant desires to sublease from Sublandlord a portion of the
Original Premises containing 11,493 rentable square feet on the third floor and
more particularly shown crosshatched on the floor plan attached hereto as
Exhibit B (the "Subleased Premises"), and Sublandlord is willing to sublease the
Subleased Premises to Subtenant on the provisions, covenants and conditions
hereinafter set forth.

                                A G R E E M E N T
                                -----------------

NOW, THEREFORE, in consideration of Ten Dollars ($10.00), the mutual covenants
made herein, and other consideration, the receipt and sufficiency of which are
hereby acknowledged and agreed, Sublandlord hereby subleases to Subtenant and
Subtenant hereby takes and hires from Sublandlord the Subleased Premises, on the
terms and conditions set forth below:

     1.       Defined Terms.  All terms defined in the Prime Lease and used
herein shall, unless otherwise defined herein, have the meanings ascribed to
such terms in the Prime Lease.

     2. Term. The term of this Sublease (the "Sublease Term") shall commence on
August 1, 2002 (the "Sublease Term Commencement Date"), and shall continue until
July 31, 2005 unless sooner terminated in accordance with the provisions of this

<PAGE>

Sublease. In addition, the Subtenant shall have a one time right to exercise an
option to extend the term of the Sublease Term for a two (2) year period of
time, commencing August 1, 2005 and terminating July 31, 2007. The monthly Base
Rent for each month of the renewal term shall be $23,129.66. Subtenant must
provide Sublandlord with written notice of Subtenant's exercise of the two (2)
year option, which written notice must be delivered to Sublandlord no later than
January 1, 2005, time being made specifically and expressly hereby of the
essence for the delivery of said notice by Subtenant to Sublandlord. It is also
a precondition to the exercise of the two (2) year option period that Subtenant
be and remain current in the payment and performance of all obligations of the
Sublease, both at the time of delivery of the notice to exercise the option
period and at the commencement date of the option period.

     3. Delivery. The Subleased Premises shall be delivered to Subtenant on the
Sublease Term Commencement Date, broom-clean and free of all occupants but
otherwise "as-is, where-is and with all faults," without representation or
warranty, express or implied, and Subtenant hereby waives, disclaims and
renounces any representation or warranty. Neither Prime Landlord nor Sublandlord
shall have any obligation to make any improvements in or to the Subleased
Premises. Subtenant shall not make any improvements to the Subleased Premises
without first having obtained Prime Landlord's and Sublandlord's consent
thereto, it being understood that Prime Landlord and Sublandlord may, in their
sole discretion, withhold such consents.

     4. Base Rent. Subtenant shall pay to Sublandlord, in advance, monthly
installments, without withholding, offset or reduction, Base Rent of $22,028.25
per month commencing one month after the Sublease Term Commencement Date (the
"Rent Commencement Date"). Base Rent for any partial calendar months at the
beginning or end of the Sublease Term shall be prorated on a daily basis.
Subtenant acknowledges that Sublandlord's payments of Base Rent for the Original
Premises are paid to Prime Landlord on the first day of each calendar month
during the Term and Subtenant therefore covenants and agrees that its payments
of Base Rent hereunder shall be paid to Sublandlord at least five (5) business
days prior to the first of each calendar month.

     5. Additional Rent. Subtenant acknowledges that pursuant to Paragraph 3 (b)
of the Prime Lease, Sublandlord is obligated to pay to Prime Landlord additional
rent on account of operating costs, insurance and real estate taxes for the
Building, as more particularly described in such Paragraph. Subtenant shall pay
to Sublandlord, with its monthly payment of Base Rent from and after the Rent
Commencement Date, Subtenant's proportionate share of Sublandlord's additional
rent obligations under the Prime Lease, such proportionate share being fixed at
16.9% (the number of rentable square feet in the Subleased Premises expressed as
a percentage of the number of rentable square feet in the Original Premises);
(referred to hereinafter as "Subtenant's Proportionate Share") provided that,
for the purpose of this Sublease, the Subtenant's Base Year shall be the 2001
calendar year. Sublandlord shall deliver to Subtenant promptly after receipt
thereof any documentation and statements of operating costs, insurance or real
estate taxes delivered to Sublandlord by Prime Landlord. Additional Rent payable
hereunder for any partial calendar month at the beginning or end of the Sublease
Term shall be pro-rated on a daily basis. Upon Subtenant's written request, and
subject to the terms and conditions of the Prime Lease, Sublandlord shall cause
an audit to be conducted of Prime Landlord's books and records. Said audit shall
be conducted at the sole cost and expense of Subtenant.
<PAGE>

     6. Use.  The Subleased Premises shall be used solely for general office
use and for uses ancillary thereto, but for no other uses.

     7. Prime Lease. Subtenant agrees that it will do nothing in, on or about
the Subleased Premises which would result in the breach by Sublandlord of its
undertakings and obligations under the Prime Lease. Except as expressly set
forth herein, this Sublease shall be subject to and on all of the terms and
conditions as are contained in the Prime Lease and the provisions of the Prime
Lease are hereby incorporated into this Sublease as if Sublandlord were the
landlord thereunder and Subtenant the tenant thereunder. Where appropriate,
references to "Landlord" in the Prime Lease shall be deemed to mean
"Sublandlord" hereunder and references to "Tenant" in the Prime Lease shall be
deemed to mean "Subtenant" hereunder, it being understood and agreed that
Sublandlord will not be acting as, or assuming any of the responsibilities of,
Prime Landlord, and all references in the Prime Lease to Landlord-provided
services or Landlord insurance requirements, and any other references which by
their nature relate to the owner or operator of the Building, rather than to a
tenant of the Building subleasing space to a subtenant, shall continue to be
references to Prime Landlord and not to Sublandlord. Without limiting the
foregoing, Subtenant expressly agrees that it does not have any right to expand
the premises or extend the term under either the Sublease or the Prime Lease and
that it is not entitled to any expenditure or allowance by Sublandlord or Prime
Landlord with respect to improvements to the Subleased Premises, except as
expressly set forth herein.

     8. Subtenant's Covenants. Subtenant covenants to Sublandlord to perform all
of the covenants and obligations to be performed by Sublandlord as Tenant under
the Prime Lease as the same relate to the Subleased Premises and to comply with
this Sublease and the applicable provisions of the Prime Lease, as modified by
this Sublease, in all respects (including, without limitation, complying with
all OSHA, environmental and other applicable laws, regulations and standards).
If Subtenant shall fail to make any payment or perform any act required to be
made or performed by Subtenant under the Prime Lease pursuant to Subtenant's
assumption of Sublandlord's obligations thereunder as they relate to the
Subleased Premises, and such default is not cured by Subtenant at least three
(3) business days prior to the expiration of such Prime Lease cure period,
Sublandlord, without waiving or releasing any obligation or default hereunder,
may (but shall be under no obligation to) make such payment or perform such act
for the account and at the expense of Subtenant, and may take any and all such
actions as Sublandlord in its sole discretion deems necessary or appropriate to
accomplish such cure. If Sublandlord shall reasonably incur any expense in
remedying such default, Sublandlord shall be entitled to recover such sums upon
demand from Subtenant as Additional Rent under this Sublease.

     9. Sublandlord's Covenants. Sublandlord covenants to Subtenant to perform
all of the terms and provisions required of it under the Prime Lease and to
promptly pay when due all rents due and accruing to Prime Landlord. Sublandlord
will use reasonable efforts to enforce on behalf of Subtenant Sublandlord's
rights under the Prime Lease. Nothing contained in this Sublease shall be
construed as a guarantee by Sublandlord of any of the obligations, covenants,
warranties, agreements or undertakings of Prime Landlord in the Prime Lease, nor
as an undertaking by Sublandlord to Subtenant on the same or similar terms as
are contained in the Prime Lease.

     10. Indemnification. Subtenant shall indemnify Prime Landlord and
Sublandlord and hold them harmless from and against any and all claims, demands
suits, judgments, liabilities, costs and expenses, including reasonable
<PAGE>

attorneys fees, arising out of or in connection with Subtenant's use and
possession of the Subleased Premises, or arising out of the failure of
Subtenant, its agents, contractors or employees to perform any covenant, term
or condition of this Sublease or of the Prime Lease to be performed by Subtenant
hereunder.  Sublandlord shall indemnify Subtenant and hold Subtenant harmless
from and against any and all claims, demands, suits, judgments, liabilities,
costs and expenses, including reasonable attorneys fees, arising out of the
failure of Sublandlord to perform any covenant, term or condition of this
Sublease or of the Prime Lease to be performed by Sublandlord hereunder.

     11. Assignment and Subletting. Subtenant shall not assign this Sublease in
whole or in part or sublet the Subleased Premises in whole or in part without
the prior written consent of both Prime Landlord and Sublandlord, which consents
shall be specifically and expressly controlled by the terms of the Prime Lease.
If, as to any sublease or assignment for which Sublandlord's consent is
necessary, Subtenant receives rent or other consideration in excess of the Base
Rent and Additional Rent payable under this Sublease, Subtenant shall pay to
Sublandlord one-half of such excess, after deducting Subtenant's reasonable
legal and brokerage expenses and fit-up expenses paid for by Subtenant at the
time of such subleasing or assignment. Amounts received by Sublandlord under the
immediately preceding sentence shall, after deducting Sublandlord's reasonable
legal expenses incurred in connection therewith, be divided evenly between Prime
Landlord and Sublandlord. If Sublandlord and Prime Landlord consent to any such
assignment or subletting, Subtenant shall remain fully and primarily liable to
Sublandlord, in all respects, under the Sublease.

     12. Security Deposit. Upon the commencement of the lease, Subtenant has
delivered to Sublandlord an evergreen letter of credit issued by a federally
chartered banking institution ("Institution") in the amount of $44,056.50
("Subtenant's Security"), such letter to be held by Sublandlord as security for
the performance of Subtenant's obligations under this Sublease. Upon the
occurrence of any default by Subtenant hereunder, Subtenant agrees that
Sublandlord may draw upon all or any part of Subtenant's Security and apply the
same to any obligation of Subtenant hereunder. If all or any portion of
Subtenant's Security is applied by Sublandlord against any of Subtenant's
obligations hereunder, Subtenant shall promptly restore Subtenant's Security to
its original amount. The letter of credit shall provide, among other items, that
the Institution shall provide Sublandlord with forty-five (45) days written
notice of any election not to renew and that Sublandlord may then draw upon the
letter of credit if no suitable letter of credit is provided at least thirty
(30) days prior to expiration of the existing letter of credit.

     13. Brokers. Each of Sublandlord and Subtenant represents and warrants to
the other that it has not dealt with any broker in connection with this
Sublease, and each agrees to indemnify, defend and hold the other harmless from
and against any breach of said representation and warranty.

     14. Utilities. Subtenant shall be responsible for all utilities (including
light, plug and HVAC electricity) in the Subleased Premises, to be paid by
Subtenant to Sublandlord within ten (10) days after billing therefor.
Subtenant's payment obligation hereunder shall be equal to the utility costs for
the third floor of the Building (which third floor is separately metered) times
the then effective Subtenant's Proportionate Share. Subtenant shall be permitted
the use of heating and air conditioning 24 hours per day, 7 days per week,
<PAGE>

conditioned upon Subtenant complying with the terms and conditions of the Prime
Lease including, but not limited to, Paragraph 6, Services and Utilities,
Subparagraph (e).

     15. Parking and Signage. Subtenant shall be entitled to use Subtenant's
then applicable Proportionate Share of the parking spaces allocated to
Sublandlord under the Prime Lease, on a non-exclusive basis. Sublandlord shall
have no obligation to police the parking areas or enforce Subtenant's parking
rights hereunder. Subtenant shall be entitled to its pro-rata share of signage
rights under the Prime Lease.

     16. Miscellaneous.
         --------------

          A.   Counterparts.  This  instrument  may  be  signed  in  counterpart
               originals,  which,  taken  together,  shall  constitute  a single
               original instrument.

          B.   Notices.   Notices  to  Sublandlord  or  Subtenant   required  or
               permitted hereunder shall be sent in the manner prescribed in the
               Prime Lease to the  respective  addresses  set forth above to the
               attention  of John D.  Hamilton,  Jr.,  Chairman,  in the case of
               notices to  Sublandlord  and of H. Joseph  Reiser,  President and
               Chief Executive Officer, in the case of notices to Subtenant.

          C.   Amendments. This Sublease may not be changed or terminated orally
               but only by an  agreement in writing  signed by both  Sublandlord
               and Subtenant.

          D.   Estoppel  Certificates.  Sublandlord  and Subtenant each agree to
               furnish within twenty (20) days after written request therefor by
               the other,  a  certificate  stating (i) that this  Sublease is in
               full force and effect and has not been  amended or  modified  (or
               describing  such  amendment or  modification,  if any);  (ii) the
               dates through which Base Rent and additional  rent have been paid
               hereunder;  and (iii)  that  there  are no  defaults  under  this
               Sublease  known to the signer of the  certificate  (or specifying
               such defaults, if known).

          E.   No  Waiver.  The  failure  of  either  party to  insist on strict
               performance of any covenant or condition  hereof,  or to exercise
               any option contained  herein,  shall not be construed as a waiver
               of such covenant, condition or option in any other instance.

          F.   Memorandum of Lease.  Subtenant shall not record this Sublease or
               any memorandum hereof.

          G.   Governing Law. The parties agree that the rights and  obligations
               of  the  parties  under  this  Sublease  shall  be  governed  and
               construed in accordance with the laws of the State of New Jersey.

          H.   Severability.  The  invalidity  of any of the  provisions of this
               Sublease  will not impair or affect in any  manner the  validity,
               enforceability or effect of the rest of this Sublease.
<PAGE>

          I.   Entire  Agreement.  All  understandings  and agreements,  oral or
               written, heretofore made between the parties hereto are merged in
               this  Sublease,  which alone fully and  completely  expresses the
               agreement between Sublandlord and Subtenant.

          J.   Relationship  Between the Parties.  This Sublease does not create
               the  relationship of principal and agent,  nor does it create any
               partnership,  joint venture,  or any  association or relationship
               between Sublandlord and Subtenant other than as and to the extent
               specifically provided in this Sublease,  the sole relationship of
               Sublandlord and Subtenant being that of sublandlord and subtenant
               as provided in this Sublease.

          K.   Remedies Cumulative.  Except as specifically provided herein, all
               rights and remedies of  Sublandlord  under this Sublease shall be
               cumulative  and none shall  exclude any other rights and remedies
               allowed by law.

          L.   Condition  Precedent.  The  effectiveness  of  this  Sublease  is
               expressly  subject to and  conditional  upon the  conditions  set
               forth in Section  17 of the Prime  Lease.  Sublandlord  agrees to
               promptly  notify the Prime Landlord of this proposed  Sublease in
               accordance with Paragraph 17 of the Prime Lease.  Sublandlord and
               Subtenant  shall  cooperate  in seeking  to obtain  the  required
               consent of the Prime  Landlord.  The submission by Sublandlord to
               Subtenant of this Sublease shall have no binding force or effect,
               shall not  constitute  an option for the leasing of the Subleased
               Premises,  nor confer any rights or impose any  obligations  upon
               either  party  until the  execution  thereof by  Sublandlord  and
               Subtenant  and the delivery of an executed  original copy thereof
               to Sublandlord.

          M.   Limitation  on Liability.  Notwithstanding  any provision of this
               Sublease to the contrary, Subtenant's recourse hereunder shall be
               solely to the assets of the Sublandlord,  and no partner, member,
               shareholder,   joint  venture  partner,   retired  and  withdrawn
               partner,  retired  or  withdrawn  member,  retired  or  withdrawn
               shareholder,  directly or  indirectly,  of the  Sublandlord  (the
               "Exculpated  Parties") shall be personally liable for the payment
               or performance  of any of  Sublandlord's  obligations  under this
               Sublease  or to satisfy a  monetary  judgment  for  Sublandlord's
               failure  to make any  such  payment  or  perform  any  obligation
               hereunder.  Subtenant shall not seek any monetary damages against
               any of the Exculpated Parties in connection with this Sublease.
<PAGE>


IN WITNESS WHEREOF, the parties have executed this Sublease as an instrument
under seal as of the date first written above.

                                     SUBLANDLORD:

                                     HALE AND DORR LLP

                                     By: /s/ John D. Hamilton, Jr.
                                         ---------------------------------------
                                         John D. Hamilton, Jr.
                                         Chairman


                                     SUBTENANT:

                                     CYTOGEN CORPORATION


                                     By: /s/ H. Joseph Reiser
                                         ---------------------------------------
                                         H. Joseph Reiser
                                         President and Chief Executive Officer