<PAGE>

                              FIRST AMENDMENT TO LEASE 
                              (GENESEE EXECUTIVE PLAZA)

     THIS FIRST AMENDMENT TO LEASE ("FIRST AMENDMENT") is made and entered 
into as of the 31st day of July, 1998, by and between ARDEN REALTY LIMITED 
PARTNERSHIP, a Maryland limited partnership ("LANDLORD") and FIRSTWORLD 
COMMUNICATIONS, INC., a Delaware corporation (formerly known as SPECTRANET 
INTERNATIONAL, INC.) ("Tenant").

                                    RECITALS:

     A.   Talcott Realty I Limited Partnership, a Connecticut limited 
partnership ("ORIGINAL LANDLORD") and Tenant entered into that certain Office 
Lease, dated as of September 4, 1996 (the "Lease"), whereby Original Landlord 
leased to Tenant and Tenant leased from Original Landlord certain office 
space located in that certain building located and addressed at 9333/9339 
Genesee Avenue, San Diego, California (the "Building"). Landlord is the 
successor-in-interest to Original Landlord.

     B.   By this First Amendment, Landlord and Tenant desire to expand the 
Premises, extend the Term and to otherwise modify the Lease as provided 
herein.

     C.   Unless otherwise defined herein, capitalized terms as used herein 
shall have the same meanings as given thereto in the Lease.

     NOW, THEREFORE, in consideration of the foregoing recitals and the 
mutual covenants contained herein, and for other good and valuable 
consideration, the receipt and sufficiency of which are hereby acknowledged, 
the parties hereto hereby agree as follows:

                                    AGREEMENT:

     1.   THE EXISTING PREMISES. Landlord and Tenant hereby agree that 
pursuant to the Lease, Landlord currently leases to Tenant and Tenant 
currently leases from Landlord that certain office space in the Building 
containing 11,627 rentable (10,128 usable) square feet located on the second 
(2nd) floor of the Building located and addressed at 9333 Genesee Avenue and 
known as Suite 200 (the "EXISTING PREMISES"), as outlined on Attachment 2 to 
the Lease.

     2.   EXPANSION OF THE PREMISES. That certain space located on the first 
(1st) floor of the building located and addressed at 9333 Genesee Avenue 
consisting of 8,375 (7,295 usable) rentable square feet and known as Suite 
100 and that certain space located on the first (1st) floor of the building 
located and addressed at 9339 Genesee Avenue consisting of 15,344 rentable 
(13,366 usable) square feet and known as Suite 100, as outlined on the floor 
plan attached hereto as Exhibit "A" and made a part hereof, may be referred 
to herein as the "EXPANSION SPACE." Effective as of September 1, 1998 
("EXPANSION COMMENCEMENT DATE"), Tenant shall lease from Landlord and 
Landlord shall lease to Tenant the Expansion Space. Accordingly, effective 
upon the Expansion Commencement Date, the Existing Premises shall be 
increased to include the Expansion Space. Landlord and Tenant hereby agree 
that such addition of the Expansion Space to the Existing Premises shall, 
effective as of the Expansion Commencement Date, increase the number of 
rentable square feet leased by Tenant in the Building to a total of 35,346 
rentable square feet. Effective as of the Expansion Commencement Date, all 
references to the "Premises" shall mean and refer to the Existing Premises as 
expanded by the Expansion Space. Notwithstanding anything to the contrary 
contained herein, Tenant shall have the right to commence business from the 
Expansion Space during the period prior to the Expansion Commencement Date 
(the "EARLY OCCUPANCY PERIOD"), provided that (i) Tenant shall give Landlord 
at least ten (10) days prior notice of any such occupancy of the Expansion 
Space and (ii) all of the terms and conditions of the Lease, as amended by 
this First Amendment shall apply, including Tenant's obligations to pay 
Monthly Base Rent for the portion of the Expansion Space

<PAGE>

so utilized by Tenant (which rent shall be prorated based upon the number of 
rentable square feet of such space at Two Dollars ($2.00) per rentable square 
foot per month).

     3.   EXTENDED LEASE TERM. The Termination Date shall be extended such 
that the Lease shall terminate on August 31, 2002 ("NEW TERMINATION DATE"). 
The period from the Expansion Commencement Date through the New Termination 
Date specified above, shall be referred to herein as the "Extended Term."

     4.   MONTHLY BASE RENT. During the Extended Term, Tenant shall pay in 
accordance with the provisions of this Section 4, Monthly Base Rent for the 
entire Premises as follows:

<TABLE>
<CAPTION>
     MONTH              MONTHLY BASE RENT
     -----              -----------------
<S>                     <C>
       1                   $66,041.20
      2-12                 $66,622.55
       13                  $68,282.88
     14-24                 $73,166.22
     25-36                 $75,727.04
     37-48                 $78,377.48
</TABLE>

     5.   TENANT'S PROPORTIONATE SHARE AND BASE YEAR FOR THE EXPANSION SPACE. 
Effective as of the Expansion Commencement Date and continuing throughout the 
Extended Term (i) Tenant's Proportionate Share of any increase in Operating 
Expenses for the Expansion Space only shall be fifteen point one eight 
percent (15.18%) and (ii) the Base Year shall be the calendar year 1998.

     6.   BASE YEAR FOR THE EXISTING PREMISES. Section II.M. of the Lease is 
hereby amended to insert a Base Year for the Existing Premises of 1999, which 
Base Year shall be effective as of October 1, 1999. Notwithstanding the 
foregoing, Tenant's Proportionate Share of Excess Expenses for the Existing 
Premises for the period prior to October 1, 1999 shall be calculated based on 
a 1996 Base Year as indicated in the Lease.

     7.   TENANT IMPROVEMENTS. Tenant Improvements in the Expansion Space 
shall be installed and constructed in accordance with the terms of the Tenant 
Work Letter attached hereto as Exhibit "B" and made a part hereof. The 
construction of the Tenant Improvements will be governed by the Tenant Work 
Letter and not the terms of Section 8 of the Lease.

     8.   PARKING. Effective as of the Expansion Commencement Date and 
continuing throughout the Extended Term, Section II.T. of the Lease shall be 
amended to provide that Tenant shall rent from Landlord a total of one 
hundred twenty-seven (127) parking passes for use in the Building's parking 
facility of which one hundred nineteen (119) such passes shall be unreserved 
parking passes and the eight (8) remaining passes shall be reserved parking 
spaces. The reserved spaces shall be contiguous to Tenant's existing reserved 
spaces in the Building parking facility, but in no event shall the total 
number of reserved spaces exceed eight (8) spaces. Tenant's rental and use of 
such additional parking passes shall be in accordance with, and subject to, 
all provisions of Section 28 of the Lease; provided, however that the monthly 
parking rates for such passes shall be amended as stated herein. The parking 
passes shall be provided to Tenant free of charge from the Expansion 
Commencement Date through February 29, 2000. Commencing on March 1, 2000, all 
unreserved parking passes rented by Tenant shall be at the rate of 
Twenty-five Dollars ($25.00) per unreserved pass per month and the reserved 
parking spaces shall be at the rate of Fifty Dollars ($50.00) per pass per 
month.

     9.   SECURITY DEPOSIT. Tenant has previously deposited with Landlord 
Eighteen Thousand Twenty-One and 85/100 Dollars ($18,021.85) as a Security 
Deposit under the Lease. Concurrently with Tenant's execution of this First 
Amendment, Tenant shall deposit with Landlord an additional Forty-Eight 
Thousand Six Hundred and 70/100 Dollars ($48,600.70), for a total Security 
Deposit under the Lease, as amended herein, of Sixty-Six Thousand Six Hundred

                                         -2-
<PAGE>

Twenty-Two and 55/100 Dollars ($66,622.55). Landlord shall continue to hold 
the Security Deposit as increased herein in accordance with the terms and 
conditions of Attachment 1, Section 24 of the Lease.

     10.  SIGNAGE/DIRECTORY.

          10.1  LOBBY/SUITE SIGNAGE.  Provided Tenant is not in default under 
the Lease (as amended by this First Amendment), Tenant, at Tenant's sole cost 
and expense, shall have the right to two (2) lines in the lobby directory of 
the Building during the Extended Term. In addition, provided Tenant is not in 
default under the Lease (as amended by this First Amendment), Tenant shall 
have the right, at Tenant's sole cost and expense (or as a charge to the 
Improvement Allowance pursuant to the Tenant Work Letter attached hereto as 
Exhibit "B"), to install Building standard suite signage designated by 
Landlord ("TENANT'S SIGNAGE"). Tenant's Signage shall be subject to 
Landlord's approval as to size, design, location, graphics, materials, colors 
and similar specifications and shall be consistent with the exterior design, 
materials and appearance of the Building and the Building's signage program 
and shall be further subject to all applicable local governmental laws, 
rules, regulations, codes and other governmental approvals and any applicable 
covenants, conditions and restrictions. Tenant's Signage shall be personal to 
the Original Tenant (as defined in Section II below) and may not be assigned 
to any assignee or sublessee, or any other person or entity. Landlord has the 
right, but not the obligation, to oversee the installation of Tenant's 
Signage. Upon the expiration of the Extended Term, or other earlier 
termination of the Lease, as amended by this First Amendment, Tenant shall be 
responsible for any and all costs associated with the removal of Tenant's 
Signage, including, but not limited to, the cost to repair and restore the 
Building to its original condition, normal wear and tear excepted.

          10.2  BUILDING TOP SIGNAGE.  Subject to this Section 10.2, Tenant 
shall be entitled to install, at its sole cost and expense, one (1) sign on 
the exterior of the Building identifying Tenant, at the highest point 
possible on the building ("SIGNAGE"). The graphics, materials, size, color, 
design, lettering, lighting (if any), specifications and exact location of 
the Signage (collectively, the "SIGNAGE SPECIFICATIONS") shall be subject to 
the prior written approval of Landlord, which approval should not be 
unreasonably withheld. In addition, the Signage and all Signage 
Specifications therefore shall be subject to (i) Tenant's receipt of all 
required governmental permits and approvals, (ii) all applicable governmental 
laws and ordinances, (iii) any existing sign rights of other tenants of the 
Building and (iv) all covenants, conditions and restrictions affecting the 
Building. Tenant hereby acknowledges that, notwithstanding Landlord's 
approval of the Signage and/or the Signage Specifications therefor, Landlord 
has made no representations or warranty to Tenant with respect to the 
probability of obtaining such approvals and permits. In the event Tenant does 
not receive the necessary permits and approvals for the Signage, Tenant's and 
Landlord's rights and obligations under the remaining provisions of the 
Lease, as amended by this First Amendment, shall not be affected. The cost of 
installation of the Signage, as well as all costs of design and construction 
of such Signage and all other costs associated with such Signage, including, 
without limitation, permits, maintenance and repair, shall be the sole 
responsibility of Tenant. Notwithstanding anything to the contrary contained 
herein, in the event that at any time during the Extended Term (or any Option 
Term, if applicable), Tenant fails to occupy at least 35,346 rentable square 
feet in the building, Tenant's right to the Signage shall thereupon terminate 
and Tenant shall remove such Signage as provided in this Section 10.2 below. 
The rights to the Signage shall be personal to the Original Tenant and may 
not be transferred. Should the Signage require maintenance or repairs as 
determined in Landlord's reasonable judgment, Landlord shall have the right 
to provide written notice thereof to Tenant and Tenant shall cause such 
repairs and/or maintenance to be performed within thirty (30) days after 
receipt of such notice from Landlord at Tenant's sole cost and expense. 
Should Tenant fail to perform such maintenance and repairs within the period 
described in the immediately preceding sentence, Landlord shall have the 
right to cause such work to be performed and to charge Tenant, as Additional 
Rent, for the cost of such work. Upon the expiration or earlier termination 
of the Lease, as amended by this First Amendment and any applicable Option 
Term (or the termination of Tenant's Signage right as described above), 
Tenant shall, at Tenant's sole cost and expense, cause the Signage to be 
removed from the exterior of the Building and shall cause the exterior of the 
Building to be restored to the condition existing prior to the placement of 
such Signage. If Tenant fails to remove such Signage and to restore the 
exterior of the Building as provided in the

                                         -3-
<PAGE>

immediately preceding sentence within thirty (30) days following the 
expiration or early termination of the Lease, as amended by this First 
Amendment, then Landlord may perform such work, and all costs and expenses 
incurred by Landlord in so performing such work shall be reimbursed by Tenant 
to Landlord within ten (10) days after Tenant's receipt of invoice therefor. 
The immediately preceding sentence shall survive the expiration or earlier 
termination of the Lease, as amended by this First Amendment. Any signs, 
notices, logos, pictures, names or advertisements which are installed and 
that have not been individually approved by Landlord may be removed without 
notice by Landlord at the sole expense of Tenant. Except as provided in this 
Section 10 above, Tenant may not install any signs on the exterior or roof of 
the Building or the common areas of the Building or the Land.

     11.  OPTION TO EXTEND. Section II.G. of the Lease is hereby deleted in 
its entirety and in lieu thereof Landlord hereby grants to the Tenant named 
herein (the "ORIGINAL TENANT") one (1) option ("OPTION") to extend the 
Extended Term for a period of four (4) years ("OPTION TERM"), which option 
shall be exercisable only by written notice delivered by Tenant to Landlord 
set forth below. The rights contained in this Section 11 shall be personal to 
the Original Tenant and may only be exercised by the Original Tenant (and not 
any assignee, sublessee or other transferee of the Original Tenant's interest 
in the Lease, as amended herein) if the Original Tenant occupies the entire 
Existing Premises and Expansion Space as of the date of Tenant's Acceptance 
(as defined in Section 11(b) below).

     (a)  OPTION RENT.  The rent payable by Tenant during the Option Term 
("OPTION RENT") shall be equal to the "Market Rent" (defined below). "MARKET 
RENT" shall mean the applicable Monthly Base Rent, including all escalations, 
operating expenses, additional rent and other charges at which tenants, as of 
the commencement of the Option Term, are leasing non-sublease, 
non-encumbered, space comparable in size, location and quality to the 
Premises in renewal transactions for a term comparable to the Option Term 
which comparable space is located in office buildings comparable to the 
Building in the University Towne Center area, taking into consideration the 
value of the existing improvements in the Premises to Tenant, as compared to 
the value of the existing improvements in such comparable space, with such 
value to be based upon the age, quality and layout of the improvements and 
the extent to which the same could be utilized by Tenant with consideration 
given to the fact that the improvements existing in the Premises are 
specifically suitable to Tenant.

     (b)  EXERCISE OF OPTION.  The Option shall be exercised by Tenant only 
in the following manner: (i) Tenant shall not be in default, and shall not 
have been in default under the Lease, as amended herein, more than once after 
the expiration of any applicable cure periods, on the delivery date of the 
Interest Notice and Tenant's Acceptance; (ii) Tenant shall deliver written 
notice ("INTEREST NOTICE") to Landlord not more than twelve (12) months nor 
less than nine (9) months prior to the New Termination Date stating that 
Tenant is interested in exercising the Option; (iii) within fifteen (15) 
business days of Landlord's receipt of Tenant's written notice, Landlord 
shall deliver notice ("OPTION RENT NOTICE") to Tenant setting forth the 
Option Rent; and (iv) if Tenant desires to exercise such Option, Tenant shall 
provide Landlord written notice within fifteen (15) days after receipt of the 
Option Rent Notice ("TENANT'S ACCEPTANCE") and upon and concurrent with such 
exercise, Tenant may, at its option, object to the Option Rent contained in 
the Option Rent Notice. Tenant's failure to deliver the Interest Notice or 
Tenant's Acceptance on or before the dates specified above shall be deemed to 
constitute Tenant's election not to exercise the Option. If Tenant timely and 
properly exercises its Option, the Extended Term shall be extended for the 
Option Term upon all of the terms and conditions set forth in the Lease, as 
amended herein, except that the rent for the Option Term shall be as 
indicated in the Option Rent Notice unless Tenant, concurrently with Tenant's 
Acceptance, objects to the Option Rent contained in the Option Rent Notice, 
in which case the parties shall follow the procedure and the Option Rent 
shall be determined, as set forth in Section 11(c) below.

     (c)  DETERMINATION OF MARKET RENT.  If Tenant timely and appropriately 
objects to the Market Rent in Tenant's Acceptance, Landlord and Tenant shall 
attempt to agree upon the Market Rent using their best good-faith efforts. If 
Landlord and Tenant fail to reach agreement within twenty-one (21) days 
following Tenant's Acceptance ("OUTSIDE AGREEMENT DATE"), then each party 
shall make a separate determination of the Market Rent which shall be 
submitted to each other and to arbitration in accordance with the following 
items (i) through (vii):

                                         -4-
<PAGE>


          (i)    Landlord and Tenant shall each appoint, within ten (10) days 
of the Outside Agreement Date, one arbitrator who shall by profession be a 
current real estate broker or appraiser of commercial high-rise properties in 
the immediate vicinity of the Project, and who has been active in such field 
over the last five (5) years. The determination of the arbitrators shall be 
limited solely to the issue of choosing either Landlord's or Tenant's 
submitted Market Rent as the deemed Market Rent, taking into account the 
requirements of item (b), above.

          (ii)   The two arbitrators so appointed shall within five (5) 
business days of the date of the appointment of the last appointed arbitrator 
agree upon and appoint a third arbitrator who shall be qualified under the 
same criteria set forth hereinabove for qualification of the initial two 
arbitrators.

          (iii)  The three arbitrators shall within fifteen (15) days of the 
appointment of the third arbitrator reach a decision as to whether the 
parties shall use Landlord's or Tenant's submitted Market Rent, and shall 
notify Landlord and Tenant thereof.

          (iv)   The decision of the majority of the three arbitrators shall 
be binding upon Landlord and Tenant.

          (v)    If either Landlord or Tenant fails to appoint an arbitrator 
within ten (10) days after the applicable Outside Agreement Date, the 
arbitrator appointed by one of them shall reach a decision, notify Landlord 
and Tenant thereof, and such arbitrator's decision shall be binding upon 
Landlord and Tenant.

          (vi)   If the two arbitrators fail to agree upon and appoint a 
third arbitrator, or both parties fail to appoint an arbitrator, then the 
appointment of the third arbitrator or any arbitrator shall be dismissed and 
the matter to be decided shall be forthwith submitted to arbitration under 
the provisions of the American Arbitration Association, but subject to the 
instruction set forth in this item (c).

          (vii)  The cost of arbitration shall be paid by Landlord and Tenant 
equally.

     12.  ASSIGNMENT AND SUBLETTING.  Section 16(c) of Attachment I to the 
Lease is hereby amended to provide that, in the event of an assignment or 
sublease, Tenant shall pay to Landlord fifty percent (50%) of all sums 
referred to in Sections 16(c)(1) and 16(c)(2) of the Lease.

     13.  BROKERS.  Each party represents and warrants to the other that no 
broker, agent or finder negotiated or was instrumental in negotiating or 
consummating this First Amendment other than CB Richard Ellis, Inc. Each 
party further agrees to defend, indemnify and hold harmless the other party 
from and against any claim for commission or finder's fee by any entity who 
claims or alleges that they were retained or engaged by the first party or at 
the request of such party in connection with this First Amendment.

     14.  SIGNING AUTHORITY.  Concurrently with Tenant's execution of this 
First Amendment, Tenant shall provide to Landlord a copy of a resolution of 
the Board of Directors authorizing the execution of this First Amendment on 
behalf of Tenant, which copy of resolution shall be duly certified by the 
secretary or an assistant secretary of the corporation to be a true copy of a 
resolution duly adopted by the Board of Directors of said corporation and 
shall be in the form of Exhibit "C" or in some other form reasonably 
acceptable to Landlord. In the event Tenant fails to comply with the 
requirements set forth in this Section 14, then each individual executing 
this First Amendment shall be personally liable for all of Tenant's 
obligations in the Lease (as amended by this First Amendment).

     15.  DEFAULT. Tenant hereby represents and warrants to Landlord that, as 
of the date of this First Amendment, Tenant is in full compliance with all 
terms, covenants and conditions of the Lease and that there are no breaches 
or defaults under the Lease by Landlord or Tenant, and that Tenant knows of 
no events or circumstances which, given the passage of time, would constitute 
a default under the Lease by either Landlord or Tenant.

     16.  WAIVER OF JURY TRIAL. EACH PARTY HEREBY WAIVES ANY RIGHT TO TRIAL 
BY JURY IN ANY ACTION SEEKING SPECIFIC PERFORMANCE OF ANY PROVISION OF THE 
LEASE (AS AMENDED BY THIS FIRST

                                         -5-
<PAGE>

AMENDMENT), FOR DAMAGES FOR ANY BREACH UNDER THE LEASE (AS AMENDED BY THIS 
FIRST AMENDMENT), OR OTHERWISE FOR ENFORCEMENT OF ANY RIGHT OR REMEDY UNDER 
THE LEASE (AS AMENDED BY THIS FIRST AMENDMENT).

     17.  NO FURTHER MODIFICATION. Except as set forth in this First 
Amendment, all of the terms and provisions of the Lease shall apply with 
respect to the Expansion Space and shall remain unmodified and in full force 
and effect. Effective as of the Expansion Commencement Date, all references 
to the "Lease" shall refer to the Lease as amended by this First Amendment.

     IN WITNESS WHEREOF, this First Amendment has been executed as of the day 
and year first above written.


"LANDLORD"

                                      ARDEN REALTY LIMITED PARTNERSHIP, 
                                      a Maryland limited partnership


                                      By:  ARDEN REALTY, INC.,
                                           a Maryland corporation
                                           Its:  Sole General Partner


                                           By: /s/ Victor J. Coleman
                                               ------------------------------
                                               VICTOR J. COLEMAN
                                               Its:  President and COO


                                           By: /s/ Andrew J. Sobel
                                               ------------------------------
                                               ANDREW J. SOBEL
                                               Its:  Exec. V.P. and 
                                                     Assistant Secretary

"TENANT"

                                      FIRSTWORLD COMMUNICATIONS, INC.
                                      a Delaware corporation


                                      By:  /s/ Bob Cerasoli
                                           ----------------------------------
                                      Print Name:  BOB CERASOLI
                                                Title: Senior Vice President


                                      By:  /s/ G. Bradford Saunders
                                           ----------------------------------
                                      Print Name:  G. BRADFORD SAUNDERS
                                                Title: Asst. Sec.

                                         -6-
<PAGE>

                                     EXHIBIT "A"

                            OUTLINE OF EXPANSION SPACE




                                        [MAP]



                                     EXHIBIT "A"

                                        1 OF 2
<PAGE>

                                     EXHIBIT "A"

                            OUTLINE OF EXPANSION SPACE




                                        [MAP]



                                     EXHIBIT "A"

                                        2 OF 2
<PAGE>

                                     EXHIBIT "B"

                                  TENANT WORK LETTER

     This Tenant Work Letter shall set forth the terms and conditions 
relating to the renovation of the tenant improvements in the Existing 
Premises and the Expansion Space. This Tenant Work Letter is essentially 
organized chronologically and addresses the issues of the construction of the 
Existing Premises and the Expansion Space, in sequence, as such issues will 
arise.

                                     SECTION 1

               LANDLORD'S INITIAL CONSTRUCTION IN THE EXPANSION SPACE

     Landlord has constructed, at its sole cost and expense, the base, shell 
and core (i) of the Expansion Space, and (ii) of the floor of the Building on 
which the Expansion Space is located (collectively, the "BASE, SHELL AND 
CORE"). Tenant has inspected and hereby approves the condition of the 
Expansion Space and the Existing Premises and the Base, Shell and Core, and 
agrees that the Expansion Space and the Existing Premises and the Base, Shell 
and Core shall be delivered to Tenant in their current "as-is" condition. The 
renovation to the improvements in the Expansion Space and the Existing 
Premises shall be designed and constructed pursuant to this Tenant Work 
Letter.

                                     SECTION 2

                                    IMPROVEMENTS

     2.1  IMPROVEMENT ALLOWANCE,  Tenant shall be entitled to a one-time 
improvement allowance (the "IMPROVEMENT ALLOWANCE") in the amount of 
$335,761.80 (based on $13.80 per usable square foot of the Expansion Space 
and $5.00 per usable square foot of the Existing Premises) for the costs 
relating to the initial design and construction of Tenant's improvements 
which are permanently affixed to the Expansion Space and Existing Premises 
(the "IMPROVEMENTS"). In no event shall Landlord be obligated to make 
disbursements pursuant to this Tenant Work Letter in a total amount which 
exceeds the Improvement Allowance and in no event shall Tenant be entitled to 
any credit for any unused portion of the Improvement Allowance not used by 
Tenant by February 1, 1999. Allocation of the Improvement Allowance between 
the Expansion Space and the Existing Premises shall be determined in Tenant's 
reasonable discretion.

     2.2  DISBURSEMENT OF THE IMPROVEMENT ALLOWANCE.  Except as otherwise set 
forth in this Tenant Work Letter, the Improvement Allowance shall be 
disbursed by Landlord (each of which disbursements shall be made pursuant to 
Landlord's disbursement process provided below) for costs related to the 
construction of the Improvements and for the following items and costs 
(collectively, the "IMPROVEMENT ALLOWANCE ITEMS"): (i) payment of the fees of 
the "Architect" and the "Engineers," as those terms are defined in Section 
3.1 of this Tenant Work Letter, and payment of the fees incurred by, and the 
cost of documents and materials supplied by, Landlord and Landlord's 
consultants in connection with the preparation and review of the 
"Construction Drawings," as that term is defined in Section 3.1 of this 
Tenant Work Letter, (ii) the cost of permits and construction supervision 
fees; (iii) the cost of any changes in the Base, Shell and Core required by 
the Construction Drawings; (iv) the cost of any changes to the Construction 
Drawings or Improvements required by applicable building codes (the "CODE"); 
and (v) the "Landlord Coordination Fee," as that term is defined in Section 
4.3 of this Tenant Work Letter. However, in no event shall more than $3.00 
per usable square foot for the Expansion Space and $1.50 per usable square 
foot for the Existing Premises of the Improvement Allowance be used for the 
items described in (i) and (ii) above; any additional amount incurred as a 
result of (i) and (ii) above shall be deemed to constitute an Over-Allowance 
Amount. During the construction of the Improvements, Landlord shall make 
monthly disbursements of the Improvement Allowance for Improvement Allowance 
Items for the benefit of Tenant and shall authorize the release of monies for 
the benefit of Tenant as follows.

                                     EXHIBIT "B"
<PAGE>

          2.2.1   MONTHLY DISBURSEMENTS.  On or before the first day of each 
calendar month, during the construction of the Improvements (or such other 
date as Landlord may designate), Tenant shall deliver to Landlord: (i) a 
request for payment of the "Contractor," as that term is defined in Section 
4.1 of this Tenant Work Letter, approved by Tenant, in a form to be provided 
by Landlord, showing the schedule, by trade, of percentage of completion of 
the Improvements in the Expansion Space and the Existing Premises, detailing 
the portion of the work completed and the portion not completed; (ii) 
invoices from all of "Tenant's Agents," as that term is defined in Section 
4.2 of this Tenant Work Letter, for labor rendered and materials delivered to 
the Expansion Space and the Existing Premises; (iii) executed mechanic's lien 
releases from all of Tenant's Agents which shall comply with the appropriate 
provisions, as reasonably determined by Landlord, of California Civil Code 
Section 3262(d); and (iv) all other information reasonably requested by 
Landlord. Tenant's request for payment shall be deemed Tenant's acceptance 
and approval of the work furnished and/or the materials supplied as set forth 
in Tenant's payment request. Thereafter, Landlord shall deliver a check to 
Tenant in payment of the lesser of (A) the amounts so requested by Tenant, as 
set forth in this Section 2.2.1, above, less a ten percent (10%) retention 
(the aggregate amount of such retentions to be known as the "FINAL 
RETENTION"), and (B) the balance of any remaining available portion of the 
Improvement Allowance (not including the Final Retention), provided that 
Landlord does not dispute any request for payment based on non-compliance of 
any work with the "Approved Working Drawings," as that term is defined in 
Section 3.4 below, or due to any substandard work, or for any other reason. 
Landlord's payment of such amounts shall not be deemed Landlord's approval or 
acceptance of the work furnished or materials supplied as set forth in 
Tenant's payment request.

          2.2.2.  FINAL RETENTION.  Subject to the provisions of this Tenant 
Work Letter, a check for the Final Retention payable to Tenant shall be 
delivered by Landlord to Tenant following the completion of construction of 
the Expansion Space and the Existing Premises, provided that (i) Tenant 
delivers to Landlord properly executed mechanics lien releases in compliance 
with both California Civil Code Section 3262(d)(2) and either Section 
3262(d)(3) or Section 3262(d)(4), (ii) Landlord has determined that no 
substandard work exists which adversely affects the mechanical, electrical, 
plumbing, heating, ventilating and air conditioning, life-safety or other 
systems of the Building, the curtain wall of the Building, the structure or 
exterior appearance of the Building, or any other tenant's use of such other 
tenant's leased premises in the Building and (iii) Architect delivers to 
Landlord a certificate, in a form reasonably acceptable to Landlord, 
certifying that the construction of the Improvements in the Expansion Space 
and the Existing Premises has been substantially completed.

          2.2.3   OTHER TERMS.  Landlord shall only be obligated to make 
disbursements from the Improvement Allowance to the extent costs are incurred 
by Tenant for Improvement Allowance Items. All Improvement Allowance Items 
for which the Improvement Allowance has been made available shall be deemed 
Landlord's property.

     2.3  STANDARD TENANT IMPROVEMENT PACKAGE. Landlord has established 
specifications (the "SPECIFICATIONS") for the Building-standard components to 
be used in the construction of the Improvements in the Expansion Space and 
the Existing Premises (collectively, the "STANDARD IMPROVEMENT PACKAGE"), 
which SPECIFICATIONS are available upon request. The quality of Improvements 
shall be equal to or of greater quality than the quality of the 
Specifications, provided that Landlord may, at Landlord's option, require the 
Improvements to comply with certain Specifications.

                                     SECTION 3

                               CONSTRUCTION DRAWINGS

     3.1  SELECTION OF ARCHITECT/CONSTRUCTION DRAWINGS.  Tenant shall retain 
KMA Architects as its architect/space planner which architect/space planner 
has been reasonably approved by Landlord (THE "ARCHITECT") to prepare the 
"Construction Drawings," as that term is defined in this Section 3.1. Tenant 
shall also retain the engineering consultants designated by Landlord (the 
"ENGINEERS") to prepare all plans and engineering working drawings relating 
to the structural, mechanical, electrical, plumbing, HVAC and lifesafety work 
of the Improvements. The

                                     EXHIBIT "B"

                                         -2-
<PAGE>

plans and drawings to be prepared by Architect and the Engineers hereunder 
shall be known collectively as the "CONSTRUCTION DRAWINGS." All Construction 
Drawings shall comply with the drawing format and specifications as 
reasonably determined by Landlord, and shall be subject to Landlord's 
reasonable approval. Tenant and Architect shall verify, in the field, the 
dimensions and conditions as shown on the relevant portions of the base 
building plans, and Tenant and Architect shall be solely responsible for the 
same, and Landlord shall have no responsibility in connection therewith. 
Landlord's review of the Construction Drawings as set forth in this Section 
3, shall be for its sole purpose and shall not imply Landlord's review of the 
same, or obligate Landlord to review the same, for quality, design, Code 
compliance or other like matters. Accordingly, notwithstanding that any 
Construction Drawings are reviewed by Landlord or its space planner, 
architect, engineers and consultants, and notwithstanding any advice or 
assistance which may be rendered to Tenant by Landlord or Landlord's space 
planner, architect, engineers, and consultants, Landlord shall have no 
liability whatsoever in connection therewith and shall not be responsible for 
any omissions or errors contained in the Construction Drawings.

     3.2  FINAL SPACE PLAN.  Tenant and the Architect shall prepare the final 
space plan for Improvements in the Expansion Space and the Existing Premises 
(collectively, the "FINAL SPACE PLAN"), which Final Space Plan shall include 
a layout and designation of all offices, rooms and other partitioning, their 
intended use, and equipment to be contained therein, and shall deliver the 
Final Space Plan to Landlord for Landlord's approval.

     3.3  FINAL WORKING DRAWINGS.  Architect and the Engineers shall complete 
the architectural and engineering drawings for the Expansion Space and the 
Existing Premises, and the final architectural working drawings in a form 
which is complete to allow subcontractors to bid on the work and to obtain 
all applicable permits (collectively, "FINAL WORKING DRAWINGS") and shall 
submit the same to Landlord for Landlord's approval.

     3.4  PERMITS.  The Final Working Drawings shall be approved by Landlord 
(the "APPROVED WORKING DRAWINGS") prior to the commencement of the 
construction of the Improvements. Tenant shall cause the Architect to 
immediately submit the Approved Working Drawings to the appropriate municipal 
authorities for all applicable building permits necessary to allow 
"Contractor," as that term is defined in Section 4.1, below, to commence and 
fully complete the construction of the Improvements (the "PERMITS"). No 
changes, modifications or alterations in the Approved Working Drawings may be 
made without the prior written consent of Landlord, which consent shall not 
be unreasonably withheld.

                                     SECTION 4

                          CONSTRUCTION OF THE IMPROVEMENTS

     4.1  CONTRACTOR.  A general contractor shall be retained by the Tenant 
to construct the Improvements. Such general contractor ("CONTRACTOR") shall 
be Neilson Dillingham or, in the event Landlord does not approve the 
qualifications of Neilson Dillingham (which are to be provided to Landlord 
for review), another general contractor shall be selected by Tenant and 
approved by Landlord.

     4.2  TENANT'S AGENTS.  All subcontractors, laborers, materialmen, and 
suppliers used by the Tenant (such subcontractors, laborers, materialmen, and 
suppliers, and the Contractor to be known collectively as "TENANT'S AGENTS") 
must be approved in writing by Landlord, which approval shall not be 
unreasonably withheld or delayed. If Landlord does not approve any of the 
Tenant's proposed subcontractors, laborers, materialmen or suppliers, the 
Tenant shall submit other proposed subcontractors, laborers, materialmen or 
suppliers for Landlord's written approval. In addition, Landlord reserves the 
right to require that any and all subcontractors be selected by a competitive 
bidding process. Notwithstanding the foregoing, the Tenant shall be required 
to utilize subcontractors designated by Landlord for any mechanical, 
electrical, plumbing, life-safety, sprinkler, structural and air-balancing 
work.

     4.3  CONSTRUCTION OF IMPROVEMENTS BY CONTRACTOR.  The Tenant shall 
independently retain, in accordance with Section 4.1 above, Contractor to 
construct the Improvements in

                                      EXHIBIT "B"

                                         -3-
<PAGE>

accordance with the Approved Working Drawings. The Tenant shall pay, or the 
Improvement Allowance shall be charged, a logistical coordination fee (the 
"LANDLORD COORDINATION FEE") to Landlord in an amount equal to five percent 
(5%) of the total amount of the construction contract and general conditions 
between the Tenant and the Contractor.

     4.4  INDEMNIFICATION & INSURANCE.

          4.4.1   INDEMNITY.  Tenant's indemnity of Landlord as set forth in 
Article 10 of the Lease shall also apply with respect to any and all costs, 
losses, damages, injuries and liabilities related in any way to any act or 
omission of Tenant or Tenant's Agents.

          4.4.2   REQUIREMENTS OF TENANT'S AGENT.  Each of Tenant's Agents 
shall guarantee to Tenant and for the benefit of Landlord that the portion of 
the Improvements for which it is responsible shall be free from any defects 
in workmanship and materials for a period of not less than one (1) year from 
the date of completion thereof. All such warranties or guarantees as to 
materials or workmanship of or with respect to the Improvements shall be 
contained in the contract or subcontract and shall be written such that such 
guarantees or warranties shall inure to the benefit of both Landlord and 
Tenant, as their respective interests may appear, and can be directly 
enforced by either. Tenant covenants to give to Landlord any assignment or 
other assurances which may be necessary to effect such right of direct 
enforcement.

          4.4.3   INSURANCE REQUIREMENTS.

                  4.4.3.1   GENERAL COVERAGES.  All of Tenant's Agents shall 
carry worker's compensation insurance covering all of their respective 
employees, and shall also carry public liability insurance, including 
property damage, all with limits, in form and with companies as are required 
to be carried by Tenant as set forth in Section 9 of the Lease.

                  4.4.3.2   SPECIAL COVERAGES.  Tenant shall carry "Builder's 
All Risk" insurance in an amount approved by Landlord covering the 
construction of the Improvements, and such other insurance as Landlord may 
require. Such insurance shall be in amounts and shall include such extended 
coverage endorsements as may be reasonably required by Landlord.

                  4.4.3.3   GENERAL TERMS.  Certificates for all insurance 
carried pursuant to this Section 4.4.3.3 shall be delivered to Landlord 
before the commencement of construction of the Improvements and before the 
Contractor's equipment is moved onto the site. In the event that the 
Improvements are damaged by any cause during the course of the construction 
thereof, Tenant shall immediately repair the same at Tenant's sole cost and 
expense. Landlord may, in its discretion, require Tenant to obtain a lien and 
completion bond or some alternate form of security satisfactory to Landlord 
in an amount sufficient to ensure the lien-free completion of the 
Improvements and naming Landlord as a co-obligee.

                                     SECTION 5

                                   MISCELLANEOUS

     5.1  TENANT'S REPRESENTATIVE.  The Tenant has designated Linda Armstrong 
as its sole representative with respect to the matters set forth in this 
Tenant Work Letter, who, until further notice to Landlord, shall have full 
authority and responsibility to act on behalf of the Tenant as required in 
this Tenant Work Letter.

     5.2  LANDLORD'S REPRESENTATIVE.  Prior to commencement of construction 
of Improvements, Landlord shall designate a representative with respect to 
the matters set forth in this Tenant Work Letter, who, until further notice 
to the Tenant, shall have full authority and responsibility to act on behalf 
of the Landlord as required in this Tenant Work Letter.

     5.3  TIME OF THE-ESSENCE IN THIS TENANT WORK LETTER. Unless otherwise 
indicated, all references herein to a "number of days" shall mean and refer 
to calendar days.

                                     EXHIBIT "B"

                                         -4-
<PAGE>

     5.4  FINAL DRAWINGS PROVIDED TO LANDLORD.  Notwithstanding anything to 
the contrary contained herein, upon completion of the Improvements pursuant 
to this Tenant Work Letter, Tenant shall provide Landlord with complete 
copies of all Construction Drawings, including, but not limited to, the 
Approved Working Drawings, which drawings shall be in a form approved by 
Landlord, but which shall be a reproducible form (i.e. C.A.D. discs) for 
Landlord's records and use.

     5.5  COMPLETION OF IMPROVEMENTS DURING THE EXTENDED TERM.  Tenant 
hereby agrees and acknowledges that the Improvements in the Expansion Space 
and/or the Existing Premises shall be constructed during the Term of the 
existing Lease and/or the Extended Term hereof and that the performance of 
such work shall not be deemed a constructive eviction nor shall Tenant be 
entitled to any abatement of Rent in connection therewith.

     5.6  INDEPENDENT HVAC SYSTEM.  Landlord and Tenant hereby acknowledge 
that Tenant may, as part of the Improvements to be performed in accordance 
with this Tenant Work Letter, install in the that part of the Expansion Space 
known as Suite 100 of the building located and addressed at 9339 Genesee 
Avenue ("HVAC SPACE"), an independent heating, ventilation and air 
conditioning system ("HVAC SYSTEM"), the electricity for which shall be 
separately metered at Tenant's sole cost and expense and for which Tenant 
shall make payment directly to the entity providing such electricity. Tenant 
shall, at Tenant's sole cost and expense, maintain a service and/or 
maintenance contract for such HVAC System with a contractor reasonably 
approved by Landlord, which contractor shall perform all maintenance and 
repairs on the HVAC System. Tenant hereby acknowledges that the HVAC System 
shall be part of the Improvements constructed in accordance with this Tenant 
Work Letter and shall be deemed Landlord's property upon the expiration or 
earlier termination of the Lease, as amended by this First Amendment, in 
accordance with Section 2.2.3 above. 

                                      EXHIBIT "B"

                                         -5-
<PAGE>

                                     EXHIBIT "C"

                                 CERTIFIED COPY OF
                           BOARD OF DIRECTORS RESOLUTIONS
                                         OF
                          FIRSTWORLD COMMUNICATIONS, INC.

     The undersigned, being the duly elected Corporate Secretary of 
Firstworld Communications, Inc., a Delaware corporation ("CORPORATION"), 
hereby certifies that the following is a true, full and correct copy of the 
resolutions adopted by the Corporation by unanimous written consent in lieu 
of a special meeting of its Board of Directors, and that said resolutions 
have not been amended or revoked as of the date hereof.

     RESOLVED, that the Corporation, is hereby authorized to execute, deliver 
and fully perform that certain document entitled First Amendment to Lease 
("AMENDMENT") by and between the Corporation and Arden Realty Limited 
Partnership, a Maryland limited partnership, for the lease of space at 9333 
and 9339 Genesee Avenue.

     RESOLVED FURTHER, that the Corporation is hereby authorized and directed 
to make, execute and deliver any and all, consents, certificates, documents, 
instruments, amendments, confirmations, guarantees, papers or writings as may 
be required in connection with or in furtherance of the Amendment 
(collectively with the Amendment, the "DOCUMENTS") or any transactions 
described therein, and to do any and all other acts necessary or desirable to 
effectuate the foregoing resolution.

     RESOLVED FURTHER, that the following officers acting together: 
_____________ as ____________ and _______________ as ______________ are 
authorized to execute and deliver the Documents on behalf of the Corporation, 
together with any other documents and/or instruments evidencing or ancillary 
to the Documents, and in such forms and on such terms as such officer(s) 
shall approve, the execution thereof to be conclusive evidence of such 
approval and to execute and deliver on behalf of the Corporation all other 
documents necessary to effectuate said transaction in conformance with these 
resolutions.


Date:                , 199
     ----------------     --       -------------------------------------------
                                              , Corporate Secretary
                                   -----------




                                      EXHIBIT "C"