SIXTH MODIFICATION OF LEASE

     AGREEMENT (herein this "Sixth Lease  Modification"),  made this 11th day of
August,  1998,  by and between SBC HOLDINGS  L.P.,  having their office and Post
Office Address c/o National Realty & Development  Corp., 3 Manhattanville  Road,
Purchase,  New York 10577 (hereinafter referred to as "Landlord") and OSTEOTECH,
INC., a Delaware corporation,  having an office at 51 James Way, Eatontown,  New
Jersey 07724 (hereinafter referred to as "Tenant").

                              W I T N E S S E T H:

         WHEREAS, Landlord (as successor-in-interest to Robert C. Baker, et al.)
and Tenant are parties to that  certain  Lease dated August 18, 1986 as modified
by First Modification of Lease dated May 31, 1989, Second  Modification of Lease
dated December 22, 1989, Third Modification of Lease dated June 21, 1991, Fourth
Modification  of Lease dated  January 30, 1992 and Fifth  Modification  of Lease
dated  October 16, 1996  between  Landlord and Tenant (said lease as modified is
hereinafter referred to as the "Lease") respecting certain premises (hereinafter
referred to as the "DEMISED  PREMISES")  within the buildings  commonly known as
1151  Shrewsbury  Avenue and 1163  Shrewsbury  Avenue (the  "Buildings")  in the
BOROUGH OF SHREWSBURY, COUNTY OF MONMOUTH and STATE OF NEW JERSEY which premises
are more particularly described in the Lease; and

     WHEREAS,  the parties  hereto desire to further modify the Lease in certain
respects as hereafter provided.

     NOW, THEREFORE, in consideration of ONE AND 00/100 ($1.00) DOLLAR and other
good and  valuable  consideration,  each to the  other in hand  duly  paid,  the
receipt and sufficiency whereof is hereby acknowledged, it is mutually agreed as
follows:

     1. The Plot Plan of 1163 Shrewsbury  Avenue presently  annexed to the Lease
as  Exhibit  "A-1"  is  hereby  deleted  therefrom  and  the  Plot  Plan of 1163
Shrewsbury Avenue annexed hereto as Exhibit "A-1" is hereby  substituted in lieu
thereof.  The attached  Exhibit "A-1" shows an area consisting of  approximately
7,750  square  feet  located in the  building  known as 1163  Shrewsbury  Avenue
situated within Lot No. 3/1, which area is cross-hatched on Exhibit "A-1" and is
hereinafter  referred to as the "Additional  Premises".  Upon the Effective Date
(as hereinafter defined),  the Additional Premises shall be deemed to be part of
the Demised Premises,  as if originally included



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within the Demised  Premises,  as the same is defined by the Lease.  The overall
square  footage of the Demised  Premises  shall be  increased  to  approximately
36,710 square feet.  Tenant has examined the Additional  Premises and has made a
complete  inspection  of the same and is familiar  with the  physical  condition
thereof  as of  this  date.  Landlord  has  not  made  and  does  not  make  any
representation  as to the physical  condition  or any other matter  affecting or
relating to the Additional  Premises except as provided below.  Tenant agrees to
accept the Additional Premises "as-is".

     2. The  Effective  Date  shall be the date  upon  which  Landlord  delivers
possession of the Additional Premises to Tenant .

     3. The Term of the Lease is hereby extended to that date which is the tenth
(10th)  anniversary of the last day of the calendar month in which the Effective
Date shall occur (the "Expiration Date").

     4. From and after the Effective  Date,  the annual  minimum  rental payable
pursuant to Article 3 of the Lease,  and in  accordance  with and subject to the
provisions  of the Lease,  shall be as follows  (subject  to the  provisions  of
Paragraph 7 hereof):

          (A) From the  Effective  Date  through  the day before the Fifth (5th)
          anniversary  of the Effective  Date:  THREE HUNDRED EIGHT THOUSAND SIX
          HUNDRED  SEVENTY AND 00/100  ($308,670.00)  DOLLARS per annum - TWENTY
          FIVE THOUSAND SEVEN HUNDRED TWENTY TWO AND 50/100 ($25,722.50) DOLLARS
          per month.  Notwithstanding  the foregoing,  in consideration  for the
          performance of Tenant's Work (as  hereinafter  defined),  Tenant shall
          receive a rent credit of $15,000.00 against the rentals payable during
          the  month  next  following  the date upon  which  Tenant  shall  have
          completed the Tenant's  Work and shall have  delivered to Landlord the
          documentation required pursuant to Paragraph 5 below:

          (B) From the Fifth (5th) anniversary of the Effective Date through the
          Expiration Date: THREE HUNDRED FORTY FOUR THOUSAND THREE HUNDRED FORTY
          AND 00/100 ($344,340.00) DOLLARS per annum - TWENTY EIGHT THOUSAND SIX
          HUNDRED NINETY FIVE AND 00/100 ($28,695.00) DOLLARS per month.


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     5. Following written notice given by Landlord to Tenant after the Effective
Date (such notice is hereinafter  called the "Landlord's  Work Notice"),  Tenant
shall  perform,  in the  Additional  Premises and the  premises  adjacent to the
Additional  Premises (which  adjacent  premises are designated on Exhibit A-1 as
the  "Remaining  Programmer's  Paradise  Space") the work described in Exhibit B
annexed hereto.  Within thirty (30) days from the date of execution and delivery
of this Sixth Lease Modification,  Tenant shall prepare and submit plans for the
Tenant's Work to Landlord for Landlord's  approval.  Tenant covenants and agrees
that Tenant shall commence the  performance of the Tenant's Work within ten (10)
days  following  Tenant's  receipt of notice from  Landlord  that  Landlord  has
approved the plans and  specifications for the performance of the Tenant's Work,
and thereafter Tenant shall diligently prosecute such Tenant's Work and complete
same as soon as  possible,  but in no event more than  thirty (30) days from and
after the date of the  Landlord's  Work Notice.  Tenant's Work shall be effected
solely in  accordance  with the plans and  specifications  approved by Landlord.
Tenant's Work shall be performed in accordance with all of the provisions of the
Lease,  including,  without  limitation,  the provisions of Articles 6, 7 and 19
thereof. During the progress of Tenant's Work, Tenant's Work shall be subject to
inspection by representatives of Landlord, who shall be permitted access and the
opportunity to inspect at all reasonable  times, but this provision shall not in
any way whatsoever create any obligation on Landlord to conduct an inspection or
impose any liability on Landlord for the failure of any such Tenant's Work. Upon
completion  of  Tenant's  Work,  Tenant  shall  submit to  Landlord  in form and
substance satisfactory to Landlord and counsel for Landlord the following:

          (a) A Certificate  of Completion by a licensed  architect or engineer,
     which  Certificate  shall certify that all Tenant's Work has been completed
     in accordance with the approved plans and specifications;

          (b) A certificate  by Tenant that the entire cost of Tenant's Work has
     been paid and the  amount  thereof,  that all those who  furnished  work or
     materials  have been paid in full,  and that no party has filed any lien or
     possesses any claim which is unpaid or remains undischarged;

          (c)  A  Certificate   of  Occupancy,   or  an  equivalent   permit  or
     certificate,  required by any governmental authorities for the occupancy of
     the Additional Premises and the Remaining Programmer's Paradise Space;


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          (d) A final  release  and  lien  waiver  signed  by  Tenant's  general
     contractor  and  all  subcontractors  and  materialmen,   together  with  a
     certificate  by the  general  contractor  to the effect  that all those who
     furnished  work or materials to the  Additional  Premises and the Remaining
     Programmer's Paradise Space have been paid in full and that the release and
     waiver has been signed by all those who furnished  work or materials to the
     Additional Premises and the Remaining Programmer's Paradise Space; and

          (e) Final and complete "as-built" plans (architectural and mechanical)
     evidencing the Tenant's  Work. 

     In the  event  that  Landlord  shall  determine,  in its sole and  absolute
discretion,  that Tenant is not proceeding  diligently  with the  performance of
Tenant's Work or has otherwise defaulted in its obligations under this Paragraph
4 or under the Lease,  in addition to any other  remedies that Landlord may have
under the Lease as a result of Tenant's default,  Landlord shall have the right,
but shall not be obligated to, perform the Tenant's Work on Tenant's  behalf and
at Tenant's sole cost and expense. Tenant shall reimburse Landlord,  within five
(5) days following billing therefor, for any and all costs and expenses incurred
by Landlord  (including  administrative and overhead charges) in the performance
of Tenant's Work.

     6.  Notwithstanding  anything to the contrary  contained  therein,  Section
31.01 of the Lease is hereby  modified to provide  that for the purposes of this
Lease,  as of the Effective  Date,  15,197 square feet is deemed to be leased as
office  space and 21,513  square  feet is deemed to be leased as  non-office  or
processing space.

     7. Landlord and Tenant  acknowledge  that,  pursuant to letter dated May 6,
1998,   Tenant  has  exercised  its  option  under  paragraph  3  of  the  Fifth
Modification  of Lease dated  October 16, 1996 between  Landlord and Tenant,  to
lease the approximate  7,040 square foot premises  presently  occupied by Asbury
Park Press at 1151  Shrewsbury  Avenue,  which leasing shall  commence,  and the
annual minimum rental payable under the Lease shall increase, from and after the
date  that   Landlord   delivers   possession   of  such   premises  to  Tenant.
Notwithstanding  anything to the contrary set forth in paragraph 3 of said Fifth
Modification  of Lease,  in the event  that the lease of the  Asbury  Park Press
premises commences following the Effective Date of this Sixth Lease Modification
(as defined  herein),  the annual minimum rental amount set forth in Paragraph 3
(b) (ii) (A) of said Fifth Modification of Lease shall be changed to $366,750.00
per annum ($30,562.50 per month), and the



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annual  minimum  rental  amount  set forth in  3(b)(ii)(B)  shall be  changed to
$409,950.00  per  annum  ($34,162.50  per  month).  Similarly,   notwithstanding
anything  to the  contrary  set forth in this Sixth Lease  Modification,  if the
Effective Date (as defined herein) occurs following the commencement date of the
leasing of the Asbury Park Press  premises (as determined by paragraph 3 of said
Fifth  Modification  of Lease),  the annual  minimum  rental amount set forth in
Paragraph 4(A) of this Sixth Lease  Modification shall be changed to $366,750.00
per annum  ($34,162.50  per month),  and the annual  minimum rental set forth in
4(B)  of  this  Sixth  Lease   Modification  shall  be  changed  to  $409,950.00
($34,162.50 per month).  Upon the commencement date of the leasing of the Asbury
Park Press premises  following the Effective Date, the overall square footage of
the Demised Premises shall be increased to 43,750 square feet, and Section 31.01
of the Lease shall be modified to provide  that for the  purposes of this Lease,
17,504  square feet is deemed to be leased as office  space,  and 26,246  square
feet is deemed to be leased as non-office space or processing space.

     8.  Tenant   acknowledges   that,  as  of  the  Effective  Date,   Tenant's
proportionate  share  of  additional  rent  payable  under  the  Lease  shall be
adjusted,  pursuant to the terms of the Lease,  to reflect  the  increase in the
square footage of the Demised Premises.

     9. In the event that the  Effective  Date has not  occurred  within one (1)
year from the date hereof,  thereafter  Landlord or Tenant shall have the right,
upon notice given by the other prior to the Effective  Date,  to terminate  this
Sixth Lease  Modification.  Notwithstanding  anything to the  contrary set forth
herein, upon termination of this Sixth Lease  Modification,  Landlord and Tenant
shall be released from all obligations  under this Sixth Lease  Modification and
the  Lease  shall  remain  in full  force  and  effect  as if this  Sixth  Lease
Modification had not been entered into between Landlord and Tenant.


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     10. Except as expressly modified herein, all of the provisions,  covenants,
conditions  and  agreements  set forth in the Lease shall continue in full force
and effect.

     IN WITNESS  WHEREOF,  the parties  have caused this Sixth  Modification  of
Lease to be executed as of the day and year first above written.

ATTEST:                                  SBC HOLDINGS L.P.,
                                         a Delaware limited partnership

                                     By: SBC BUILDING CORP.,
                                         a Delaware corporation, General Partner




/s/ Ava Saltis                           By:    /s/ Robert C. Baker
----------------------------                    --------------------------------
                                         Title: President
                                                --------------------------------







ATTEST:                                  OSTEOTECH, INC.




/s/ Steven T. Sobieski                   By:    /s/ Michael Jeffries
----------------------------                    --------------------------------
Treasurer                                       Exec. Vice President


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<PAGE>


STATE OF NEW YORK          )
                            SS:
COUNTY OF WESTCHESTER      )

     BE IT  REMEMBERED,  that on this 11th day of August,  1998,  before me, the
subscriber, A Notary Public of the State of New York, personally appeared Robert
C. Baker, President of SBC BUILDING CORP., general partner of SBC HOLDINGS L.P.,
who, I am  satisfied,  is the person  who  signed the within  instrument;  and I
having first made known to him the contents thereof,  he thereupon  acknowledged
that he  signed,  sealed  with  the  corporate  seal,  and  delivered  the  said
instrument  as such officer  aforesaid,  and that the within  instrument  is the
voluntary act and deed of said  corporation  as general  partner of SBC HOLDINGS
L.P., made by virtue of the authority of its board of directors.


                                       /s/ Richard A. Kaufman
                                       -----------------------------------------
                                       NOTARY PUBLIC


                                       Stamp: RICHARD A. KAUFMAN
                                              Notary Public, State of New York
                                              No. 4875196
                                              Qualified in Westchester County
                                              Commission Expires October 6, 1998




STATE OF  NEW JERSEY       )
                            SS:
COUNTY OF  MONMOUTH        )

     BE IT  REMEMBERED,  that on this 14th day of July,  1998,  before  me,  the
subscriber,  personally  appeared Michael J. Jeffries,  EVP of OSTEOTECH,  INC.,
who, I am  satisfied,  is the person  who  signed the within  instrument;  and I
having first made known to him the contents thereof,  he thereupon  acknowledged
that he  signed,  sealed  with  the  corporate  seal,  and  delivered  the  said
instrument  as such officer  aforesaid,  and that the within  instrument  is the
voluntary act and deed of said  corporation,  made by virtue of the authority of
its board of directors.


                                       /s/ Linda Manning Savoca
                                       -----------------------------------------
                                       NOTARY PUBLIC


                                       Stamp: LINDA MANNING SAVOCA
                                              Notary Public of New Jersey
                                              No. 2102832, Ocean County
                                              Commission Expires July 27, 2002



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                                   EXHIBIT A-1



             Diagram/Map of the Plot Plan of 1163 Shrewsbury Avenue



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                           Map of Existing Osteotech


<PAGE>



                                    EXHIBIT B


                                  TENANT'S WORK

Tenant  agrees  to  perform  the work set  forth  below in  accordance  with the
provisions of the Lease and the attached Sixth Modification of Lease.

1.   Construct or restore fire wall to separate the Additional Premises from the
     Remaining Programmer's Paradise Space.

2.   Re-paint office portion of the Remaining  Programmer's  Paradise Space (two
     coats - choice of color by Programmer's Paradise).

3.   Tenant will include in its building  plans for the Tenant's Work a new 8' x
     8' (or smaller,  at the option of  Programmer's  Paradise) UPS door, at the
     rear of the warehouse, it being understood,  however, that the construction
     of such door is not part of Tenant's Work.

4.   Tenant shall  separate and provide for separate  metering of the  utilities
     for the Additional Premises and the Remaining  Programmer's Paradise Space,
     inclusive  of the HVAC  system  which  shall be divided in a  proportionate
     manner between the two premises.

5.   Tenant shall  remove  mezzanine  shelving  platforms  used by  Programmer's
     Paradise in the  Additional  Premises,  and reinstall same in the Remaining
     Programmer's Paradise Space.

6.   The doors which will be removed by Tenant to restore the fire wall shall be
     delivered to Programmer's Paradise immediately upon their removal.

7.   Tenant  will  remove  and  replace  carpeting  (selection  by  Programmer's
     Paradise -  comparable  to  existing)  in the office area of the  Remaining
     Programmer's Paradise Space.

8.   Tenant shall coordinate the performance of Tenant's Work with  Programmer's
     Paradise, as needed, including scheduling and performing Tenant's Work in a
     manner  that will  minimize  any  disruption  in the conduct of business by
     Programmer's Paradise in the Remaining Programmer's Paradise Space.



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