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                                                                  Exhibit 10-1

                                  THE JBG COMPANIES

June 16, 1997

VIA 2-DAY MAIL

Mr. David Ruppe
PSINet, Inc.
460 Spring Park Place
Suite 100
Herndon, Virginia 20170

Re:  PSINet, Inc. at Spring Park Technology Center

Dear Mr. Ruppe:

     Enclosed for your files, please find one (1) fully executed original
Amendment No. 1 to Deed of Lease for PSINet, Inc.'s 15,076 square feet of
space located on the lower level of 460 Spring Park Place.

     Mr. Ruppe, thank you once again for the opportunity to address PSINet,
Inc.'s office requirements. In the meantime, please do not hesitate to
contact me or Tom Finan with any questions, comments or concerns.

Sincerely,

THE JBG COMPANIES


Joanna Athey
Administrative Assistant

CC W/ ENCLOSURE:    MR. STEVE RANCK, CHARLES E. SMITH COMPANIES
                    MR. ESKO KORHONEN, THE CARLYLE GROUP
                    MR. GUY STEWART, III, THE STEWART INVESTMENT COMPANY
                    MR. TOM FINAN, JBG
                    MR. CHRIS WEEMS, JBG
                    MS. LISA RITENOUR, JBG
                    MS. CHERIE STEINBACHER, JBG
                    NEGOTIATION FILE

CC W/O ENCLOSURE:   MS. HOLLY DAVIS MARSH, JBG

                                           
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                           AMENDMENT NO. 1 TO DEED OF LEASE

     THIS AMENDMENT NO. 1 TO DEED OF LEASE (the "First Amendment") is made as of
the 12th day of June, 1997, by and between JBG/Spring Park Limited
Partnership, a Virginia limited partnership("Landlord"), as successor Landlord
to TCW REALTY FUND II HOLDING COMPANY, a California corporation,
and PSINET, INC., a New York corporation ("Tenant").

                                      RECITALS:

     WHEREAS, Landlord and Tenant are parties to that certam Deed of Lease
("Lease") dated February 5, 1996, pursuant to which Landlord has leased to
Tenant and Tenant has leased from Landlord approximately 14,200 square feet (the
"Premises") in the building known as 460 Spring Park Place, Herndon, Virginia
("Building").

     WHEREAS, in January of 1997 Tenant properly exercised its right to
terminate the Lease with respect to the Premises effective July 31, 1997 
and Landlord agreed to same.

     WHEREAS, Landlord and Tenant desire to reinstate the Lease and amend same
to (i) replace the original 14,200 square feet with 15,076 square feet (the
"Replacement Premises") (ii) extend the term of the lease on the Replacement
Premises (iii) provide a Refurbishment Allowance for the Replacement Premises
and (iv) waive the early termination penalty of three (3) months rent as
outlined in Paragraph 27.22 (ii) (b) of the Lease.

     WHEREAS, all capitalized terms set forth herein, unless otherwise defined
herein, shall have the meanings ascribed to them in the Lease.

     NOW THEREFORE, in consideration of the mutual covenants and agreements
herein contained and for other good and valuable consideration, the receipt and
suff~ciency of which are hereby acknowledged, the parties hereto agree that the
Lease is hereby amended as follows:

     Section 1.    Substitution of Premises with Replacement Premises.

             1.01  As a replacement for the Premises, Landlord hereby leases
to Tenant and Tenant hereby leases from Landlord 15,076 rentable square feet of
space in the Building, as shown on the cross-hatched area of Exhibit A attached
hereto and made a part hereof (hereinafter referred to as the "Replacement
Premises").

                                           
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             1.02     As of the Replacement Premises Commencement Date, the
Replacement Premises is hereby substituted for and constitutes the Premises
defined in the Lease and is subject to all conditions of the Lease, except as
otherwise provided m this First Amendment.

    Section 2.     Commencement Date and Term as to the Replacement Premises.

         2.01  The "Replacement Premises Commencement Date" shall be
July 26, 1997 and the expiration date shall be September 17, 2003
("Replacement Premises Expiration Date") unless the Lease or this First
Amendment is terminated sooner pursuant to any provision thereof.

         2.02   Tenant shall have access to the Replacement Premises, at
no charge, for furniture and cable installation commencing June 15, 1997. 

    Section 3.  Construction and Delivery of the Replacement Premises.

         3.01  Landlord and Tenant agree that Tenant shall accept the
Replacement Premises in its "as-is", "where is" condition, except for
latent defects, on the Replacement Premises Commencement Date.
Notwithstanding the foregoing, after the Replacement Premises Commencement
Date, Landlord shall provide Tenant with an allowance of Three and
OO/lOOths Dollars ($3.00) per rentable square foot of the Replacement
Premises ("Refurbishment Allowance") for the refurbishment of the
Replacement Premises ("Refurbishment") which Refurbishment Allowance shall
be paid to Tenant by Landlord upon Landlord's receipt of paid invoices for
such Refurbishment and, in the event Tenant contracted for the performance
of any of the Refurbishment, lien waivers form all such contractors. In the
event the cost of the Refurbishment exceeds the Refurbishment Allowance,
such excess costs shall be paid in full by Tenant. In the event any portion
of the Refurbishment Allowance remains after payment of the costs described
above ("Excess Refurbishment Allowance"), Tenant may submit other moving
related invoices to Landlord for reimbursement.

         3.02     Notwithstanding the foregoing, Landlord represents that
the HVAC systems serving the Replacement Premises are in good working order
as of the date hereof and any required service will be completed prior to
the Replacement Premises Commencement Date.


                                         -2-
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    Section 4.   Base Rent for the Replacement Premises.

         4.01    Commencing on the Replacement Premises Commencement
Date, Tenant shall pay Base Rent as set forth below.

     LEASE YEAR                              MONTHLY INSTALLMENT
-------------------------                   ----------------------
    8/1/97-7/31/98                                $17,274.58
    8/1/98-7/31/99                                $17,965.57 
    8/1/99-7/31/00                                $18,684.19
    8/1/00-7/31/01                                $19,431.56
    8/1/01-7/31/02                                $20,208.82
    8/1/02-7/31/03                                $21,017.17 
    8/1/03-10/31/03                               $21,857.86
              
              

    Section 5.     Additional Rent for the Replacement Premises. 

              (i) Commencing on the Replacement Premises Commencement
Date, Section 1.9 and 1.10 of the Lease shall be deleted in their entirety 
and the following inserted in their place:

         "1.9 Tenant's Proportionate Share of Park Common Area Maintenance
         Expenses("PCAM"). 4.20% of the PCAM (which percentage is based
         upon the Replacement Premises containing 15,076 gross rentable
         square feet of the total Park containing 359,323 gross rentable
         square feet).

         1.10 Tenant's Proportionate Share of Real Estate Taxes.  11.97%
         of Real Estate Taxes(which percentage is based upon the
         Replacement Premises containing 15,076 gross rentable square feet
         of the total of buildings 450 Spring Park Place and 460 Spring
         Park Place which comprise the lot used for tax purposes by
         Fairfax County and the Town of Herndon containing 125,942 gross
         rentable square feet).

         (ii) In addition, Section 1.10A shall be inserted into the Lease:

         1.10A Tenant Proportionate Share of Building Operating Expenses 
         ("BOE"). BOE shall consist of all Landlord's actual cost of water, 
         sewer, roof repairs, and roof maintenance, and non-tenant building 
         electricity for 460 Spring Park Place only. Tenant's share of the 
         BOE shall be 23.59% (which percentage is based upon the Replacement 
         Premises containing 15,076 gross rentable square feet of the total 
         Building containing 63,912 gross rentable square feet). Expenses 
         included in the BOE as defincd above, shall be excluded from PCAM, 
         as defined in Article 7 of the Lease. In addition, the rights and 
         obligations set forth in Paragraphs 7.5 and 7.6 of the Lease shall 
         apply to the BOE.

    Section 6.     Security Deposit.

              Simultaneously with the execution of this First Amendment, 
Tenant shall deposit with Landlord an additional $7,807.91 which sum shall be 
added to the current Security Deposit (i.e., $9,466.67) held under, and in 
accordance with, the Lease resulting in a total Security Deposit of 
$17,274.58.

                                         -3-
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    Section 7.     Early Termination Option.

              Section 27.22 Early Termination Option of the Lease shall be 
deleted in its entirety and be of no further force and effect as of the date 
of this First Amendment with respect to the Replacement Premises, however, 
Landlord hereby waives Tenant's obligation to pay any penalty as outlined in 
Paragraph 27.22 (ii) (b) otherwise due as a result of the January 1997 
Termination Notice.

    Section 8. Right of First Refusal. For the first six months following the 
Replacement Premises' Commencement Date, Tenant shall have the Right Of First 
Refusal for lease of that certain space in the Building known as Suite 1000 
and containing approximately 3,531 gross rentable square feet (the "Offer 
Space"). The notice given by Landlord to Tenant shall describe the Offer 
Space, the date as of which such Offer Space shall be available for lease and 
the terms and conditions which are equal to a third party tenant's offer 
received by the Landlord under which Landlord is willing to lease such Offer 
Space. 

Tenant shall have fifteen (15) business days from the date of such notice 
from Landlord to notify Landlord that Tenant intends to enter into an 
amendment to this Lease with Landlord so as to include the Offer Space on 
such terms and conditions. Provided that Tenant shall have given the notice 
described in the preceding sentence to Landlord before the expiration of such 
fifteen (15) business day period of time, Tenant shall have fifteen (15) 
business days from the date of such notice from Landlord to enter into an 
amendment to this Lease with Landlord so as to include the Offer Space on 
such terms and conditions. If Tenant does not give notice of its intention to 
enter into such amendment with Landlord as aforesaid or does not enter into 
such amendment as aforesaid with Landlord, Landlord shall have the right to 
enter into a lease with any third party for the Offer Space on any terms and 
conditions as upon which Landlord and such third party shall agree. The 
rights extended in Section 8 to Tenant by Landlord are exclusively granted by 
Landlord to the original Tenant named under this Lease, PSINET, Inc. and any 
"affiliate" of PSINET, Inc. (as such term is defined in Section 11.1 of this 
Lease), and shall not inure to the benefit of or be exercisable by any 
assignee of the original Tenant named under this Lease other than such an 
"affiliate". Notwithstanding the foregoing, Tenant's rights under this 
Section 8 shall: (a) terminate automatically upon the issuance of any notice 
of default by Landlord to Tenant with respect to any of Tenant's obligations 
under this Lease, which default shall have continued after the giving of all 
required notices and the expiration of all periods for cure herein specified; 
(b) terminate automatically upon the failure of Tenant to have given notice 
to Landlord of its intention to enter into an amendment of the Lease with 
Landlord on the terms and conditions set forth in the preceding provisions of 
this Section 8 within fifteen (15) business days after the date of the giving 
by Landlord of notice to Tenant with respect to the availability of Offer 
Space; (c) terminate automatically upon the failure or Tenant to enter into 
an amendment to this Lease with Landlord on the terms and conditions set 
forth in the preceding provisions of this Section 8 within fifteen (15) 
business days after the date of the giving by Landlord of notice to Tenant 
with respect to the availability of Offer Space and (d) terminate 
automatically as of that date which is six (6) months after the Replacement 
Premises Commencement Date. For purposes hereof, "Preferential Rights" means 
all rights of renewal, rights of first refusal, rights of first offer, rights 
to expansion space of any other rights or agreements similar or dissimilar to 
the foregoing concerning the future

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or potential leasing of the Offer Space or any portion thereof or any other 
space in the Building of which the Offer Space or any portion thereof shall 
be a part.

    Section 9. Option to Renew.

               Commencing on the Replacement Premises Commencement Date,
Section 27.23 (i) of the Lease shall be deleted and the following
inserted in its place:

               "(i) Renewal Term. Provided that there is no existing and
uncured Event of Default by Tenant under this Lease, Tenant shall have
the option to extend the Term of this Lease with respect to the entire
Replacement Premises then subject to this Lease for one (1) additional
term of five (5) years (said term being referred to hereinafter as the
"Renewal Period") upon the same terms and conditions as set forth in
this Lease, except that the Base Rent shall be calculated as set forth
below taking into account lease concessions and Tenant shall have no
further option to renew under this Section 27.23. The option shall be
exercised by written notice from Tenant to Landlord given not later
than one hundred eighty (180) days prior to the expiration of the
initial Term or previous Renewal Period."

    Section 10. Signs.

          Commencing on the Replacement Premises Commencement Date, 
Section 14 of the lease shall be deleted in its entirety and the following 
inserted in its place:

         "Except, at Tenant's expense, the pedestal sign near the entry to
the Replacement Premises which faces 470 Spring Park Place and a suite
entry located on the entry door, no sign, advertisement or notice
shall be inscribed, painted, aff~xed, placed or otherwise displayed by
Tenant on any part of the Land or the outside or the inside
(including, without limitation, the windows) of the Building or the
Premises. Any permitted signs shall be installed and maintained by
Landlord at Tenant's sole expense. If any prohibited sign,
advertisement or notice is nevertheless exhibited by Tenant, Landlord
shall have the right to remove the same, and Tenant shall pay any and
all expenses incurred by Landlord in such removal, together with
interest thereon at the Interest Rate, upon demand. Landlord shall
have the right to prohibit any sign, advertisement, notice or
statement to the public by Tenant which, in Landlord's opinion, tends
to impair the reputation of the Building or its desirability as a frst
class office building."

         Section 11. Parking.

          Commencing on the Replacement Premises Commencement 
Date, Tenant shall have the right to three (3) additional parking spaces 
(i.e. for a total of 54 spaces) which shall be unreserved, non-exclusive 
parking spaces in the Parking Facilities.

         Section 12.    Brokers.       Landlord: JBG Properties, Inc. 
                                       Tenant:   Charles E. Smith Companies.

           Landlord recognizes Brokers as the sole brokers procuring this
First Amendment and shall pay Brokers a commission therefor pursuant to separate
agreements between Brokers and Landlord. Landlord and Tenant


                                         -5-
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each represents and warrants to the other that it has not employed any broker,
agent or finder other than Brokers relating to this First Amendment. Landlord
shall indemnify and hold Tenant harmless, and Tenant shall indemnify and hold
Landlord harmless, from and against any claim for brokerage or other commission
arising from or out of any breach of the indemnitor's representation and
warranty.

    Section 13. Authority.

    Landlord and Tenant represent and warrant to each other that the person 
signing this First Amendment on its behalf has the requisite authority and 
power to execute this First Amendment and to thereby bind the party on whose 
behalf it is being signed.

    Section 14. Applicability of Lease Provisions.

     Except as otherwise provided in this First Amendment, the terms and 
provisions of the Lease shall apply to the Replacement Premises from and after 
the date of this Replacement Premises Commencement Date.

    Section 15. Ratification.

    Except as and only to the extent explicitly modified by the terms and 
provisions of this First Amendment, all terms and provisions of the Lease 
thereto are ratified and confirmed in all respects and shall hereby remain in 
full force and effect.

     Section 16. Entire Agreement. This First Amendment contains the entire
understanding of the parties with respect to the subject matters covered hereby
and may be modified only by a written instrument signed by the party against
whom enforcement of any modification is sought.

     Section 17. Effectiveness. The furnishing of the form of this First
Amendment shall not constitute an offer and this First Amendment shall become
effective upon and only upon its execution by and delivery to each party hereto.

                      [SIGNATURES APPEAR ON FOLLOWING PAGE]


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              IN WITNESS WHEREOF, Landlord and Tenant have executed this 
Amendment No. 1 to Deed of Lease and agree to be bound thereby effective as 
of the date first written above.

  WITNESS:                                LANDLORD:
    
/s/ Karen NuWick              JBG/SPRING PARK LIMITED PARJTNERSHIP
----------------              By:  JBG Real Estate Associates,VIII, Inc.,
                                   General Partner


                                   By:/s/Brian P. Coulter  (SEAL)
                                      -----------------------------------------
                                        Name: Brian P. Coulter
                                        Title: Vice President
                        
                                   Date: June 12, 1997

ATTEST/WITNESS:               TENANT:
      
                              PSINET, INC., a New York corporation


/s/ Rob S. Metzler                 By:/s/Harold S. Wills  (SEAL)
---------------                      -----------------------------------------
                                      Name: (Typed): Harold S. Wills
                                      Title: EVP & COO

                                   Date: June 10, 1997


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Exhibit 10.1  The following Exhibits and Schedules have been omitted, which
              the Company agrees to furnish supplementally to the Commission
              upon request:


      Exhibit A: Floor Plan
      Exhibit B: Additional Expansion Space Commencement Date