<PAGE>   1
                                                                   EXHIBIT 10.25


                            THIRD AMENDMENT OF LEASE

        THIS THIRD AMENDMENT OF LEASE (this "Amendment") is made this 1 day of
August, 1997 but shall be deemed effective as of June 1, 1997 (the "Effective
Date") by and between M.O.R. COLUMBIA LIMITED PARTNERSHIP, a Maryland limited
partnership ("Landlord") and MARTEK BIOSCIENCES CORPORATION, a Delaware
corporation ("Tenant").     

                                  INTRODUCTION

         A.      Landlord's predecessor in title, Aetna Life Insurance Company,
and Tenant entered into a Lease dated August 15, 1992 (the "Original Lease"),
whereby Tenant agreed to lease twenty-seven thousand one hundred fifty (27,150)
square feet (the "Original Leased Premises") in a building known as Building K
(the "Building") in an office and research and development complex known as
"Columbia Business Center" in Howard County, Maryland.  The Original Lease was
amended by a Lease Modification Agreement (the "First Amendment") dated October
14, 1993 and by a Second Lease Modification Agreement (the "Second Amendment")
dated September 22, 1994.  The Original Lease, as amended by the First
Amendment and the Second Amendment, is herein collectively referred to as the
"Lease."

         B.      Pursuant to the various expansion rights of Tenant set forth
in Article 50 of the Lease, Tenant expanded the Original Leased Premises by a
total of twelve thousand five hundred fifty-four (12,554) square feet (the
"Expansion Space") so that, as of this date, Tenant leases a total amount of
space equal to thirty-nine thousand seven hundred four square feet (39,704)
(the "Leased Premises").

         C.      Pursuant to a Consent to Sublease of Lease by and among
Landlord, Tenant and Fidelity Mortgage and Finance Co. ("Sub-Tenant"), dated
November 4, 1996, Landlord consented to the sublease by Tenant to Sub-Tenant of
six thousand two hundred seventy-one (6,271) square feet of the Leased Premises
(the "Subleased Premises").

         D.      But for this Amendment, the initial term of the Lease would
expire on October 31, 1998.

         E.      Pursuant to Article 49 of the Lease, Tenant has an option to
extend the term of the Lease.  Landlord and Tenant desire to extend the term of
the Lease for a term ending November 30, 2004.

         F.      Unless otherwise defined herein or unless the context requires
a contrary meaning, all capitalized terms used in this Amendment shall have the
meanings given to them in the Lease.

         NOW, THEREFORE, in consideration of the foregoing Introduction, which
is deemed a substantive part of this Amendment, the covenants of the parties
herein and in the Lease and
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other good and valuable consideration, the receipt and adequacy of which are
hereby acknowledged, Landlord and Tenant hereby agree as follows:

         1.      TERM. The term of the Lease is hereby extended for a term
commencing as of June 1, 1997 (the "Renewal Commencement Date") and terminating
at 11:59 p.m. on November 30, 2004 (the "Renewal Term"), unless otherwise
terminated in accordance with the provisions of the Lease, as amended hereby,
on the same terms and conditions as are set forth in the Lease except as
specifically set forth herein.

         2.      RENT. As of the Renewal Commencement Date through the Renewal
Term, Tenant shall pay Landlord Basic Annual Rent in equal monthly installments
at the times and otherwise in the manner as set forth in the Lease as follows:

<TABLE>
<CAPTION>
                RENEWAL                      BASIC            MONTHLY         RENT PER
                 YEAR                      ANNUAL RENT      INSTALLMENT      SQUAREFOOT
                 ----                      -----------      -----------      ----------
         <S>                               <C>              <C>              <C>
         June 1, 1997-May 31, 1998         $322,396.48      $26,866.37          $8.12

         June 1, 1998-May 31, 1999         $326,763.92      $27,230.33          $8.23

         June 1, 1999-May 31, 2000         $369,247.20      $30,770.60          $9.30

         June 1, 2000-May 31, 2001         $380,761.36      $31,730.11          $9.59

         June 1, 2001-May 31, 2002         $392,275.52      $32,689.63          $9.88

         June 1, 2002-May 31, 2003         $404,186.72      $33,682.23          $10.18

         June 1, 2003-May 31, 2004         $416,494.96      $34,707.91          $10.49

         June 1, 2004-November 30, 2004    $428,803.20      $35,733.60          $10.80
</TABLE>

         3.      LEASE AMENDMENTS.  Sections 49 and 50 of the Lease are hereby
deleted in their entireties and the following new Sections 49, 50 and 51 are
incorporated into the Lease:

                 "Section 49.  Expansion Option.

                          A.      Provided: (i) the Lease is in full force and
         effect, (ii) Tenant is not in breach or default (beyond any applicable
         cure period) of any monetary provision or material non-monetary
         provisions of the Lease at the time of exercising the Expansion Option
         (as hereinafter defined), and (iii) Tenant shall have given Landlord
         written notice (the "Expansion Notice") at least 120 days prior to the
         Expansion Commencement Date (as hereinafter defined) of Tenant's
         election to exercise the Expansion Option, Tenant shall have the right
         (the "Expansion Option") to lease all or any portion of any then
         available space in the Building (the "Expansion Space") as long as the
         space remaining in the Building after such expansion is leasable in
         the Landlord's reasonable discretion and any cost to demise the
         Expansion Space that exceeds Tenant's Expansion Contribution (as
         hereinafter





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<PAGE>   3


         defined) is borne by Tenant.  The Basic Annual Rent with respect to
         the Expansion Space shall be the per square foot rental rate
         applicable to the Leased Premises, subject to the same adjustments
         during the Renewal Term, or the Additional Term (as defined below), as
         the per square foot rental rate applicable to the Leased Premises, and
         shall be paid at the times and in the manner as provided with respect
         to, and in addition to, the monthly installments of Basic Annual Rent
         with respect to the Leased Premises as set forth in the Lease.  Tenant
         shall have the right to lease and occupy the Expansion Space at any
         time prior to May 31, 1998 (the "Expansion Commencement Date").

                          B.      Notwithstanding any other provision hereof,
         the following provisions shall apply to the Expansion Option and to
         Tenant's lease, if any of the Expansion Space:

                          (i)     Tenant shall not be entitled to exercise the
         Expansion Option unless at the date Tenant gives Landlord notice of
         such exercise and on the Expansion Commencement Date, Tenant is in
         possession of the Leased Premises and Tenant is not in breach or
         default (beyond any applicable cure period) of any monetary provision
         or material non-monetary provisions of the Lease;

                          (ii)    Tenant's rental of the Expansion Space shall
         be for a term commencing on the Expansion Commencement Date, and
         continuing through the balance of the Renewal Term (and of any
         subsequent renewal term if Tenant shall have exercised its renewal
         option pursuant hereto), under and subject to the terms of the Lease,
         with the same force and effect as though this Lease had originally
         provided for the rental of the Expansion Space.

                          (iii)   Landlord shall contribute Ten Dollars
         ($10.00) per square foot of the Expansion Space (the "Expansion
         Contribution"), for any improvements to be made by Landlord for Tenant
         to the Expansion Space.  At the Tenant's option, Landlord shall
         competitively bid all work to be performed in the Expansion Space or
         the Leased Premises in connection with such expansion.  Any
         improvements to be made shall be performed in accordance with
         drawings, plans and specifications prepared by Tenant and approved by
         Landlord, such approval shall not be unreasonably withheld or delayed.
         All costs in excess of the Expansion Contribution shall be paid by
         Tenant within thirty (30) days after receipt of an invoice from
         Landlord therefor.  In the event that Manekin Corporation is no longer
         involved in the ownership or management of the Building, Tenant may
         use a reputable contractor of its choice, subject to Landlord's
         reasonable approval, to perform tenant improvements in the Expansion
         Space or in the Leased Premises.

                          (iv)    From and after the Expansion Commencement
         Date, all references in the Lease to the Leased Premises shall refer
         to the aggregate of the original Leased Premises and the Expansion
         Space and all references to the area or Rentable Area of the Leased
         Premises shall, for all purposes of this Lease, be





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<PAGE>   4


         deemed to include both the area of the original Leased Premises and of
         the Expansion Space.  Tenant's Portion shall be adjusted accordingly
         to reflect the leasing of the Expansion Space.

                          (v)     Except as otherwise expressly provided in
         this Section 49, from and after the Expansion Commencement Date, all
         of the covenants and agreements set forth in the Lease shall apply to
         the Expansion Space.

                 Time is of the essence with respect to Tenant's exercise of
         its rights under this Section 49 and Tenant acknowledges that the
         Expansion Notice must be in writing and timely sent.

                 Section 50.  Right of First Offer.  Tenant shall have the
         right of first offer (the "First Offer") to lease any space in the
         Building as it becomes available (the "First Offer Space") at a Basic
         Annual Rent equal to the price per square foot rental rate Tenant is
         then paying with respect to the Leased Premises, subject to the same
         adjustments during the Renewal Term, or the Additional Term, as the
         per square foot rental rate applicable to the Leased Premises.

                 Said rent shall be payable in equal monthly installments (and
         fractions thereof), at the times and subject to the terms and
         conditions as provided with respect to, and in addition to, the
         monthly installments of the Basic Annual Rent as set forth in this
         Lease.

                 Tenant's exercise of its First Offer shall be effective only
         upon written notification by Tenant to Landlord thereof (the
         "Notice").  Such notification must be given to Landlord before the
         close of business on the tenth full calendar day after Tenant's
         receipt of Landlord's written notification to Tenant of the
         availability of the First Offer Space and the terms on which Landlord
         intends to offer the First Offer Space for rental (the "Offer").  An
         Offer does not include the exercise by another tenant of its right of
         renewal, refusal or expansion.

                 In the event Tenant fails to so notify Landlord within said
         ten calendar day period, Landlord shall be free to offer said First
         Offer Space to third parties and Tenant shall have no further rights
         in such space.

                 This First Offer is personal to Tenant and shall not be
         separated from the Lease or transferred by Tenant independently of the
         leasehold interest without the prior written consent of Landlord.

                 Notwithstanding any other provision hereof, the following
         provisions  shall apply to the First Offer and to Tenant's lease, if
         any, of the First Offer Space:

                          (i)     Tenant shall not be entitled to exercise the
         rights accorded to Tenant in the first paragraph, unless at the date
         of such exercise or at the date on





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         which Tenant's lease, if any, of the First Offer Space becomes
         effective, Tenant is in possession of the Leased Premises and Tenant
         is not in breach or default (beyond any applicable cure period) of any
         monetary provision or material non-monetary provisions of the Lease;

                          (ii)    Tenant shall have the right to lease and
         occupy the First Offer Space commencing on the date set forth in
         Landlord's Offer (the "First Offer Space Commencement Date"), and
         terminating on the termination of the Renewal Term (or of any
         subsequent renewal term if Tenant shall have exercised its renewal
         option pursuant hereto), on the same terms, conditions, and provisions
         as are in this Lease set forth, except to the extent modified by the
         Offer, with the same force and effect as though this Lease had
         originally provided for the rental of the Leased Premises and the
         First Offer Space;

                          (iii)   Landlord shall contribute for any
         improvements to be made by Landlord for Tenant to the First Offer
         Space (i) $10.00 per square foot of the First Offer Space if the First
         Offer Space Commencement Date is on or before November 30, 2000; and
         (ii) $0.17 per square foot of the First Offer Space multiplied by the
         number of months remaining in the Renewal Term as of the First Offer
         Space Commencement Date, if the First Offer Space Commencement Date is
         after November 30, 2000 (either of which is the "Offer Contribution").
         Any improvements to be made shall be performed in accordance with
         drawings, plans and specifications prepared by Tenant and approved by
         Landlord, such approval shall not be unreasonably withheld or delayed.
         At Tenant's option, Landlord shall competitively bid all work to be
         performed in the First Offer Space or the Leased Premises in
         connection with such expansion.  All costs in excess of the Offer
         Contribution shall be paid by Tenant within thirty (30) days after
         receipt of an invoice from Landlord therefor.  In the event that
         Manekin Corporation is no longer involved in the ownership or
         management of the Building, Tenant may use a reputable contractor of
         its choice, subject to Landlord's reasonable approval, to perform
         tenant improvements in the First Offer Space or the Leased Premises.

                          (iv)    The Lease shall be amended, as may be
         appropriate, to reflect the leasing of the First Offer Space; and

                          (v)     This First Offer right is subordinate to any
         previously granted rights of any tenant of the Building, including,
         without limitation, renewal rights, expansion rights, rights of
         refusal and rights of offer, or Landlord's agreement to allow any
         existing tenant of the First Offer Space to extend its Lease thereof,
         whether or not such right exists currently.

                 Time is of the essence with respect to Tenant's exercise of
         its rights under this Section 50 and Tenant acknowledges that Landlord
         requires strict adherence to the requirement that the Notice be timely
         made and in writing.





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<PAGE>   6


                 Section 51. Renewal Option.  Provided (i) this Lease is then
         in full force and effect and, (ii) Tenant is not in breach or default
         (beyond any applicable cure period) of any monetary or material
         non-monetary provisions of this Lease either on the date Tenant elects
         to renew or on the date the Additional Term (as defined below)
         commences, Tenant shall have the right to renew this Lease for one (1)
         renewal term of five (5) years (the "Additional Term"), to commence
         immediately following the expiration of the Renewal Term and to end on
         November 30, 2009, and to be on the same terms, conditions, and
         provisions as are set forth in this Lease with the same force and
         effect as though this Lease had originally provided for such an
         extended term, save that:

                         (i)     there shall be no further right of renewal,
         after the Additional Term, and

                         (ii)    the Basic Annual Rent payable with respect to
         the Leased Premises during the Additional Term shall be adjusted to
         reflect ninety-five percent (95%) of the prevailing rental rate for
         comparable space within the market area of the Building as of the
         commencement of the Additional Term (as determined below).

                 Tenant shall be deemed to have waived the right to exercise
         this renewal option unless not less than one hundred eighty (180)
         days prior to the date of termination of the Renewal Term, Tenant
         shall have notified Landlord in writing of Tenant's election to renew
         (the "Renewal Notice").  Landlord shall give Tenant written notice of
         the prevailing rental rate within thirty (30) days after Landlord's
         receipt of the Renewal Notice (the "Rent Notice").  Tenant may elect
         to have the prevailing rent determined as set forth below if it does
         not agree with Landlord's determination thereof by giving Landlord
         written notice (the "Appraisal Notice") within ten (10) days after
         Tenant's receipt of the Rent Notice.

                 Within five (5) business days after the Landlord receives the
         Appraisal Notice from Tenant, Landlord and Tenant shall give written
         notice to the other that each, at its own expense, has hired and
         appointed a disinterested real estate broker of recognized competence
         and professional experience as a broker of comparable commercial and
         industrial real estate in the Baltimore-Washington Metropolitan Area.
         The two brokers thus appointed shall mutually agree upon the
         appointment of a third broker, the cost of which shall be shared
         equally by Landlord and Tenant, which broker shall also be a
         disinterested person of recognized competence and professional
         experience as a broker of comparable commercial and industrial real
         estate in the Baltimore-Washington Metropolitan Area.  In the event
         that the two brokers shall be unable to agree, within ten (10) days
         after their appointment, on the appointment of the third broker, then
         Tenant shall choose three brokers from whom Landlord shall choose one
         who shall serve as the third broker.  Landlord shall notify Tenant of
         the selection of the third broker within ten (10) days of Tenant's
         notice to





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<PAGE>   7


         Landlord of the selection of such three brokers from which Landlord is
         to choose.  The third broker shall as promptly as possible, but in no
         event more than thirty (30) days after the date of his selection,
         conduct an appraisal of the Building for purposes of determining the
         then prevailing rental rate therein, taking into account rent
         concessions then being offered in the market area.  Upon completion of
         his appraisal, the third broker shall immediately give written notice
         to the parties hereto stating his determination, and shall furnish to
         each party hereto a copy of such determination signed by him which
         determination shall be final and binding on the parties.

                 Time is of the essence with respect to Tenant's exercise of
         its rights under this Section 51 and Tenant acknowledges that Landlord
         requires strict adherence to the requirement that the Renewal Notice
         and Appraisal Notice be timely made and in writing.

         4.      AMENDMENT. From and after the date hereof, the Lease shall be
amended and in full force and effect in such respects as are set forth in this
Amendment, and all other provisions, terms, conditions and riders of and to the
Lease in all respects shall remain in full force and effect as set forth in the
Lease.

         5.      REAFFIRMATION. Tenant hereby reaffirms and restates, and
agrees to be bound by the covenants, promises, representations and agreements
set forth in the Lease (except to the extent that they are expressly superseded
by this Amendment) as if made herein.

         6.      BINDING ON SUCCESSORS. The terms and conditions contained in
this Amendment shall bind and inure to the benefit of Landlord and Tenant, and
their respective heirs, distributees, executors, administrators and other legal
and personal representatives, successors and permitted assigns.

         7.      AUTHORITY. Tenant represents and warrants to Landlord that
Tenant is a Delaware corporation, duly organized and in good standing and
qualified to transact business in the State of Maryland, and that the name and
address of Tenant's resident agent in Maryland are CSC Lawyers Incorporating,
11 E. Chase Street, Baltimore, Maryland 21202.

         8.      COMMISSIONS. Tenant represents that Tenant has dealt directly
with, and only with, Manekin Corporation and The Fred Ezra Company as brokers
in connection with this Amendment, and that insofar as Tenant knows, no other
broker negotiated this Amendment or is entitled to any commissions in
connection with it.  Landlord agrees to pay the commissions of Manekin
Corporation and The Fred Ezra Company in accordance with its separate agreement
with said brokers.  Tenant shall hold Landlord harmless from and indemnify
Landlord for any costs incurred by Landlord arising out of any other brokers'
claim that such broker has assisted Tenant with respect to this Amendment.





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<PAGE>   8

         9.      LENDER'S CONSENT.  In connection with Landlord's refinancing
of the Project with Allstate Life Insurance Company ("Lender") in December
1995, Tenant, Landlord and Lender entered into a subordination, non-disturbance
and attornment agreement (the "SNDA") and Tenant executed an estoppel
certificate (the "Certificate").  Pursuant to Section 5 of the Certificate and
Section 5 of the SNDA, Tenant acknowledged that Lender would not be bound by
any amendments to the Lease which Lender had not approved.  As a result
thereof, this Amendment is specifically contingent on obtaining the Lender's
consent hereto.  The parties agree to seek such consent promptly after
execution of this Amendment by Tenant and, unless such consent is granted by
Lender on or before July 31, 1997, this Amendment shall, at Tenant's or
Landlord's option, be null and void and of no further force and effect.  In no
event shall this Amendment be binding upon Lender unless and until Lender
consents to its terms.

         IN WITNESS WHEREOF, Landlord and Tenant have respectively signed and
sealed this Third Amendment of Lease as of the day and year first above
written, intending to be bound as of the Effective Date.

WITNESS:                          M.O.R. COLUMBIA LIMITED PARTNERSHIP
                          
                                  By:      Manekin Columbia Limited Partnership
                          
                                  By:      RA & DM, Inc.
                          
[sig]                     
                                  By:  /s/ R. Colfax Schnorf, Jr.   [SEAL]
                                       --------------------------
                                           Name:   R. Colfax Schnorf, Jr.
                                                   ----------------------
                                           Title:  Vice President
                                                   --------------
                                                                  LANDLORD
                          
ATTEST:                           MARTEK BIOSCIENCES CORPORATION
                          
/s/ Patricia L. Francis           By: /s/ Henry Linsert, Jr.        [SEAL]
-----------------------               ----------------------
                                           Name:   Henry Linsert, Jr.
                                                   ------------------
                                           Title:  CEO
                                                   -----------------
                                                                    Tenant




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<PAGE>   9
STATE OF MARYLAND, COUNTY/CITY OF HOWARD, TO WIT:

         I HEREBY CERTIFY that on this 1st day of August 1997, before me, the
subscriber, a Notary Public of the State of Maryland and County/City of
Baltimore, personally appeared before me R. Colfax Schnorf, Jr.,  known to me or
satisfactorily proven to be the person whose name is subscribed to the foregoing
instrument, who acknowledged himself/herself to be the Vice President of RA &
DM, Inc., the general partner of Manekin Columbia Limited Partnership, the
general partner of M.O.R. COLUMBIA LIMITED PARTNERSHIP, Landlord and he/she
acknowledged the foregoing Third Amendment of Lease to be the act and deed of
said limited partnership.

         WITNESS my hand and notarial seal.


                                                            [sig]
                                                            ------------------
                                                            Notary Public

My Commission Expires: 1-22-01


STATE OF MARYLAND,COUNTY/CITY OF HOWARD, TO WIT:

         I HEREBY CERTIFY that on this 3rd day of July, 1997, before me, the
subscriber, a Notary Public of the State aforesaid and County/City of Howard,
personally appeared before me Henry Linsert, Jr., known to me or satisfactorily
proven to be the person whose name is subscribed to the foregoing instrument,
who acknowledged herself/himself to be the CEO of MARTEK BIOSCIENCES
CORPORATION, Tenant, and she/he acknowledged the foregoing Third Amendment of
Lease to be the act and deed of said corporation.

         WITNESS my hand and notarial seal.
                                                            Patricia L. Francis
                                                            -------------------
                                                            Notary Public
My Commission Expires: 7/31/98

                           [Lender's Consent Follows]





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<PAGE>   10



         Lender signs below for purposes of evidencing its consent to the terms
of the above Third Amendment of Lease.

WITNESS:                                       ALLSTATE LIFE INSURANCE COMPANY
                                
                                
Janice Gregory                                 By: Charles Mires          [SEAL]
---------------                                    ---------------------    
                                               Name:    Charles Mires
                                                        -------------------
                                               Title:   Assistant Vice Pres.
                                                        ------------------- 
                                
                                
[sig]                                          By:  Louise Walton         [SEAL]
---------------                                     -----------------
                                               Name:   Louise Walton
                                                       ----------------   
                                               Title:  Regional Mgr
                                                       ----------------

                                               its authorized signatories


Approved as of this 5 day of September, 1997.





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