<PAGE>

                           EIGHTH AMENDMENT TO LEASE        Exhibit (10)(i)
                           -------------------------

     This Eighth Amendment to Lease (this "Amendment") is made as of January 31,
2000 by and between American National Bank and Trust Company of Chicago, as
Trustee under Trust Agreement dated April 5, 1990 and known as Trust No.
110513-07 ("Landlord"), and The Northern Trust Company, an Illinois banking
corporation.

                                   Recitals
                                   --------

     A.   American National Bank and Trust Company of Chicago, as Trustee under
Trust No. 65287 ("Prior Landlord") and Tenant entered into that certain Lease
dated August 27, 1985 (the "Original Lease") as amended by that certain First
Amendment to Agreement of Lease dated August 15, 1986 (the "First Amendment"),
that certain Second Amendment to Agreement of Lease dated August 6, 1987 (the
"Second Amendment"), and that certain Third Amendment to Agreement of Lease
dated May 20, 1988 (the "Third Amendment").

     B.   The Original Lease, as amended by the First Amendment, Second
Amendment and Third Amendment, was assigned by Prior Landlord to Landlord by an
assignment dated April 6, 1990.

     C.   Landlord and Tenant further amended the Original Lease by that certain
Fourth Amendment to Agreement of Lease dated May 1, 1990, that certain Fifth
Amendment to Agreement of Lease dated January 12, 1995, that certain Sixth
Amendment to Agreement of Lease dated November 30, 1995 and that certain Seventh
Amendment dated February 24, 1998 (the "Seventh Amendment"). The Original Lease,
as amended by all of the aforedescribed amendments, is hereinafter referred to
as the "Lease." All capitalized terms used in this Amendment and not otherwise
defined shall have the meanings ascribed to them in the Lease.

     D.   Pursuant to the Lease, Tenant now leases from Landlord approximately
240,688 rentable square feet, (subject to the terms of the Seventh Amendment),
in the building located at 181 West Madison Street, Chicago, Illinois.

     E.   Landlord and Tenant have agreed to expand the Premises and wish to
confirm their agreements regarding such expansion in this Amendment.

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

     1.   20th Floor Expansion Space. Effective as of the 20th Floor Expansion
Space Commencement Date (as hereinafter defined), and continuing until March 31,
2005 (such date, the "20th Floor Expansion Space Expiration Date") (such period,
the "20th Floor Expansion Space Term"), the Premises shall be expanded to
include that certain space on the 20th floor of the Building, containing
approximately 21,804 rentable square feet and depicted on Exhibit A attached
hereto and incorporated herein by this reference (the "20th Floor Expansion
Space"). As

<PAGE>

used herein, the "20th Floor Expansion Space Commencement Date" means the
earlier to occur of (i) the date substantial completion of the Work (as defined
in Paragraph 4(c) below), or (ii) May 1,2000. As of the 20th Floor Expansion
Space Commencement Date, the Premises shall be deemed to contain, in the
aggregate, approximately 262,492 rentable square feet. Following the occurrence
of the 20th Floor Expansion Space Commencement Date, Landlord and Tenant shall
confirm in writing the 20th Floor Expansion Space Commencement Date and the 20th
Floor Expansion Space Expiration Date. From and after the date on which Tenant
executes and delivers this Amendment, Tenant shall have the right to enter the
Premises to make inspections and measurements of the space. Notwithstanding
anything to the contrary contained herein, but subject to the conditions and
requirements set forth in Paragraph 4 below, Tenant shall have the right to
enter the Premises and to begin to improve the 20th Floor Expansion Space for
Tenant's purposes from and after the date on which this Amendment is fully
executed, in which event all of the provisions of the Original Lease applicable
to occupancy of premises shall apply and be in full force and effect as to the
20th Floor Expansion Space, other than, the obligation to pay Rent, which shall
commence on the 20th Floor Expansion Space Commencement Date. Notwithstanding
the foregoing and the requirements set forth in Paragraph 4 below, Tenant shall
have the right to perform the demolition portion of its tenant improvements to
the 20th Floor Expansion Space upon Landlord's approval of Tenant's demolition
plans and contractors performing such work, which approval shall not be
unreasonably withheld and which shall be given (or denied, with specific reasons
therefor) within three (3) business days of Tenant's submission of such
information to Landlord.

     2.   20th Floor Expansion Space Base Rent. Tenant shall pay Base Rent in
consideration for the leasing of the 20th Floor Expansion Space for the 20th
Floor Expansion Space Term, in accordance with the following schedule:


<TABLE>
<CAPTION>
            Period                      Annual Base   Annual Base  Monthly Base
                                          Rent Per        Rent         Rent
                                        Square Foot
<S>                                     <C>           <C>           <C>
20th Floor Expansion Space                $21.00       $457,884.00   $38,157.00
Commencement Date to April 30, 2001
May 1, 2001 to April 30, 2002             $21.63       $471,620.52   $39,301.71
May 1, 2002 to April 30, 2003             $22.28       $485,793.12   $40,482.76
May 1, 2003 to April 30, 2004             $22.95       $500,401.80   $41,700.15
May 1, 2004 to March 31, 2005             $23.64           N/A       $42,953.88
</TABLE>

Base Rent shall be paid promptly on the first day of each and every calendar
month during the 20th Floor Expansion Space Term.

     3.   Rent Adjustments - Operating Expenses. During the 20th Floor Expansion
Space Term and with respect to the 20th Floor Expansion Space, Tenant shall pay
Tenant's Proportionate Share of Operating Expenses and Operating Expense
Deposits as described in

<PAGE>

Paragraph 5 of the Original Lease. Tenant's Proportionate Share shall be
28.5766% as of the 20th Floor Expansion Space Commencement Date. No Rent
Adjustment (as described in Paragraph 5.B) shall be payable with respect to the
leasing of the 20th Floor Expansion Space.

     4.   Condition of Space and Tenant Improvements. Tenant agrees to accept
the 20th Floor Expansion Space in its "as is" condition as of the date of this
Amendment and agrees that Landlord has made no promise, representation or
agreement regarding any improvements, alterations or renovations of the 20th
Floor Expansion Space, except that Landlord represents and warrants that, as of
the date of this Amendment, (a) the current electrical service for the 20th
floor includes an 800-amp main which shall provide Tenant with over 10 watts of
electricity per square foot of the 20th Floor Expansion Space for lights,
outlets and Tenant's supplemental heating, ventilating and air conditioning
("HVAC"), (b) there is electrical service provided as part of the basic Building
services for emergency lighting general power requirements for the basic HVAC
service, and (c) a main floor disconnect switch service feeder and wireway, a CT
cabinet, a meter socket, branch circuit relay panels, relays, conduit, wire, and
associated feeders are currently installed in the 20th Floor Expansion Premises.
Tenant shall be permitted to construct leasehold improvements to such space, and
Landlord will contribute an allowance to the cost thereof, in accordance with
the following provisions:

          (a)  Tenant shall, at Tenant's sole cost and expense (subject to the
     Allowance, as defined below), cause to be prepared and submitted to the
     Landlord for Landlord's prior approval, at such time as Tenant desires,
     plans and specifications (the "Tenant's Plans"), including, but not limited
     to, all space plans, working drawings, mechanical and engineering drawings
     disclosing all construction to be performed to build out the 20th Floor
     Expansion Space. Landlord agrees to review and either approve or disapprove
     (and noting with such disapproval the specific items not approved) Tenant's
     Plans within five (5) business days of Landlord's receipt of a complete set
     of Tenant's Plans. In the event Tenant's Plans are disapproved, Tenant
     shall revise and resubmit Tenant's Plans expeditiously and Landlord shall
     review the same and notify the Tenant of its approval or disapproval within
     three (3) business days thereafter in the same manner as required for the
     initial submittal. Landlord's approval shall not be unseasonably withheld
     or delayed. Landlord's authorized representative ("Landlord's
     Representative") for the purpose of Tenant's deliveries or to
     communications to Landlord shall be Andrew Bartucci or such other person as
     is designated by Landlord in writing. Tenant shall not commence any work in
     the 20th Floor Expansion Space until Tenant's Plans have been approved.

          (b)  Tenant is hereby granted the right to utilize contractors of
     Tenant's own choice to build out the 20th Floor Expansion Space, subject to
     Landlord's approval as to the qualifications of such contractor which shall
     not be unreasonably withheld. Landlord hereby approves Valenti, or Bulley
     Andrews. The contractor chosen by Tenant is hereinafter referred to as
     "Tenant's Contractor". All installations, alterations and additions shall
     be constructed in a good and workmanlike manner and only new and good
     grades of material shall be used. Such work performed by Tenant's
     Contractor shall comply with the Americans With Disabilities Act, and with
     all insurance requirements and all other ordinances and regulations of the
     City of Chicago or any department or

<PAGE>

     agency thereof and with the requirements of all statutes and regulations of
     the State of Illinois or any department or agency thereof. Tenant shall
     permit Landlord's Representative (and an architect or engineer designated
     by Landlord) to observe all construction operations within the 20th Floor
     Expansion Space performed by Tenant's Contractor, provided that no
     supervision fee shall be charged by Landlord. Such observation by persons
     on behalf of Landlord shall be solely and only for the benefit of Landlord.
     Tenant shall pay to the Landlord the cost of any materials purchased from
     Landlord at Landlord's actual invoice cost for said items. Tenant shall not
     be charged for hoisting. No silence or statement by any person acting on
     behalf of Landlord shall be deemed or construed as an assumption by said
     persons or Landlord of any responsibility for or in relation to the
     construction of the 20th Floor Expansion Space or any guarantee that the
     work completed within the 20th Floor Expansion Space complies with legal
     requirements, complies with Tenant's Plans, or is suitable or acceptable to
     the Tenant for Tenant's intended business purposes. Tenant shall furnish to
     Landlord, prior to commencement of any work in the 20th Floor Expansion
     Space, building permits (or such other documentation as is required by the
     City of Chicago to commence such work) and certificates of appropriate
     insurance. Upon completion of any installations, alterations or additions,
     Tenant shall furnish Landlord with building permits (to the extent not
     previously required and furnished), and with contractor's affidavits and
     full and final waivers of lien covering all labor and material expended and
     used in constructing the 20th Floor Expansion Space. Tenant shall hold
     Landlord harmless and indemnify Landlord from all claims and costs,
     damages, liens and expenses which may arise out of or are connected in any
     way with said construction by Tenant's Contractor.

          (c)  The cost of all work (the "Work") necessary to build out all of
     the 20th Floor Expansion Space (including, but not limited to, all labor,
     material, permits and working drawings and design costs) shall, subject to
     the Allowance granted herein, be the responsibility of Tenant. Landlord
     agrees to contribute an allowance of up to Three Hundred Twenty-Seven
     Thousand Sixty Dollars ($327,060.00) (the "Allowance") toward the cost of
     the Work. The Allowance shall be paid in one lump sum payment by Landlord
     to Tenant within ten (10) business days following Tenant's submission to
     Landlord of a contract or contracts evidencing that the cost of the Work
     equals or exceeds the amount of the Allowance. As the Work progresses,
     Tenant shall require and collect, and submit copies to Landlord of, general
     contractor's statements, architect certificates (as to substantial
     completion of the stages of the Work as payments are being made therefor)
     and partial and final lien waivers, as the case may be, covering all Work
     (including design costs) for which the Allowance is being used to pay costs
     thereof. Tenant shall be responsible for collecting and submitting to
     Landlord the final lien waivers from all contractors, subcontractors and
     materialmen involved in the Work. If any mechanic lien is filed with
     respect to the Work, Tenant shall cause such lien to be discharged and
     removed from public record within thirty(30) days after such filing, or
     insure or bond over such lien to Landlord's reasonable satisfaction within
     such thirty (30) day period, failing which Landlord may take whatever steps
     are reasonably necessary to do so, at Tenant's sole cost and expense.

<PAGE>

          (d)  The 20th Floor Expansion Space shall, upon expiration of the 20th
     Floor Expansion Space Term, be left by Tenant in its then "as is"
     condition, broom clean and, notwithstanding anything to the contrary
     contained in the Lease, Landlord shall have no right to require Tenant to
     remove any of the improvements made to the 20th Floor Expansion Space.

     5.   Termination Option. Subject to the terms and provisions hereinafter
set forth, Tenant shall have the one-time option to terminate the Lease, as to
the 20th Floor Expansion Space only, effective as of March 31, 2003 (such date
of termination, the "Termination Date"), which option shall be exercised, time
being of the essence, by written notice given by Tenant to Landlord no later
than December 31, 2001. Tenant's termination notice shall be accompanied by
payment to Landlord in cash or by certified or cashier's check of 50% of the
"Termination Fee" (as hereinafter defined). The other 50% of the Termination Fee
shall be paid no later than February 28, 2003. The effectiveness of Tenant's
exercise of the termination option is conditioned upon Tenant paying to Landlord
such portions of the Termination Fee by such dates. As used herein, the
"Termination Fee" shall be an amount equal to the sum of (i) the unamortized
portion (applying an interest rate of 10% per annum) of the Allowance and
leasing commissions paid by Landlord in connection with the leasing of the 20th
Floor Expansion Space, in the aggregate amount of $422,453.00, and (ii) three
(3) full months of the then escalated "gross rent" (i.e., Base Rent and
Operating Expense Deposits). No termination hereunder shall be effective unless
Tenant has paid the foregoing amounts to Landlord at the times required under
this Paragraph 5.

     If Tenant so elects to terminate this Lease as to the 20th Floor Expansion
Space, then, effective as of the Termination Date, the Lease as to the 20th
Floor Expansion Space shall be deemed to have expired by lapse of time and
Tenant shall return the 20th Floor Expansion Space to Landlord on the
Termination Date in accordance with the requirements of this Lease. All
obligations of either party to the other which accrue under the Lease as to the
20th Floor Expansion Space on or before the Termination Date shall survive such
termination and neither the exercise of such right nor such termination shall
affect Landlord's remedies on account of any default by Tenant existing prior to
the Termination Date.

     6.   Renewal Option. Landlord hereby grants to Tenant the option to extend
the 20th Floor Expansion Space Term on the same terms, conditions and provisions
as contained in this Amendment (excluding the provisions of Paragraph 4 and 5 of
this Amendment), except as otherwise provided herein, for one period of five (5)
years (such period being referred to as the "Option Period"), which option may
be exercised by Tenant independently of any other options provided for in the
Lease and notwithstanding that the Lease may terminate with respect to other
portions of the Building currently leased by Tenant. Tenant's Proportionate
Share as to the 20th Floor Expansion Space alone, is 2.3737%.

     (a)  Tenant's option to extend shall be exercisable by written notice from
     Tenant to Landlord given no later than twelve (12) months prior to the
     expiration of the 20th Floor Expansion Space Term, time being of the
     essence. If the option is not so exercised, such option shall thereupon
     expire.
<PAGE>

          (b)  Monthly Base Rent per square foot of rentable area payable during
     the Option Period shall be equal to 95% of the market rate, as determined
     the same manner as is prescribed in Section 33.D of the Original Lease.

          (c)  Tenant may only exercise this option to extend, and an exercise
     thereof shall only be effective, if at the time of Tenant's exercise and on
     the Option Period commencement date, the Lease is in full force and effect
     and Tenant is not in material default under the Lease (after expiration of
     any applicable notice and cure period). In addition to the condition set
     forth in the first sentence of this subparagraph (c), if Tenant is in
     material default under the Lease (after expiration of any applicable notice
     and cure period) within thirty (30) days prior to the Option Period
     commencement date, and has not cured or is not in the process of diligently
     curing such default prior to said commencement date, then, at Landlord's
     option, Tenant's right to exercise its option may be terminated and
     rendered null and void by notice thereof from Landlord to Tenant. No
     sublessee or assignee shall be entitled to exercise this option to renew
     the 20th Floor Expansion Space Term, except under the following
     circumstances: (i) a successor by merger or other consolidation with Tenant
     or an acquirer of substantially all of the assets of Tenant may exercise
     this option to renew, and (ii) a sublessee of the entire 20th Floor
     Expansion space for the remainder of the 20th Floor Expansion Term, or an
     assignee of the Lease (as to the 20th Floor Expansion Space) which has been
     approved by Landlord, may exercise this option to renew if and only if (A)
     Landlord agreed, at the time of granting its consent to the assignment,
     that such assignee would have the right to exercise this option, and (B)
     Tenant agreed, at the time of its assignment, to remain fully liable under
     the Lease (as to the 20th Floor Expansion Space) through the Option Period.
     Notwithstanding anything to the contrary contained herein, the terms and
     conditions of this Paragraph 6(c) shall only apply if Tenant renews the
     Lease as to the 20th Floor Expansion Space pursuant to this renewal option.
     If Tenant renews the Lease as to the 20th Floor Expansion Space pursuant to
     Section 33 of the Original Lease (as amended by the Second Amendment), this
     Paragraph 6(c) shall not apply to such renewal.

          (d)  Upon the valid exercise by Tenant of its option to extend, at the
     request of either party hereto, Landlord and Tenant shall enter into a
     written supplement to the Lease confirming the terms, conditions and
     provisions applicable to the Option Period as determined in accordance with
     the provisions of this Section, with such revisions to the Base Rent
     provisions of this Lease as may be necessary to conform those provisions to
     the rental rate applicable to the Option Period. No new options to extend
     shall be deemed to be created by a valid exercise of this extension option
     and no other provisions inapplicable to the Option Period such as, but not
     limited to, an obligation to construct or pay for construction of
     improvements or to grant rent abatements, shall be construed to govern the
     Option Period.

     7.   Brokers. Tenant represents that, except for Douglas Elliman-Beitler
and Staubach Midwest, LLC, it has not dealt with any real estate brokers in
connection with this Eighth Amendment and, to its knowledge, no broker other
than Douglas Elliman-Beitler and

<PAGE>

Staubach Midwest, LLC, initiated or participated in the negotiation of this
Eighth Amendment, submitted or showed the 20th Floor Expansion Space or any
other space in the Building to Tenant or is entitled to any commission or fee in
connection with this Eighth Amendment. Tenant hereby agrees to indemnify,
defend, and hold Landlord harmless from and against any and all claims of any
other party for broker commission or fees in connection with this Eighth
Amendment who claim to have dealt with the Tenant.

     Landlord represents that, except for Douglas Elliman-Beitler and Staubach
Midwest, LLC, it has not deal with any real estate brokers in connection with
this Eighth Amendment and, to its knowledge, no broker other than Douglas
Elliman-Beitler and Staubach Midwest, LLC, initiated or participated in the
negotiation of this Eighth Amendment, submitted or showed the 20th Floor
Expansion Space or any other space in the Building, on behalf of Landlord, to
Tenant or is entitled to any commission or fee in connection with this Eighth
Amendment. Landlord hereby agrees to indemnify, defend, and hold Tenant harmless
from and against any and all claims of Douglas Elliman-Beitler and Staubach
Midwest, LLC and any other party for broker commissions or fees in connection
with this Eighth Amendment who claim to have dealt with the Landlord.

     8.   Y2K. If any of the Building systems or other equipment are, or have
been, required to be repaired or altered to remedy interruptions or malfunctions
in services or operations caused by the so called "Y2K" problem (i.e., the
transition of such systems and equipment from 1999 operation to 2000 operation),
Landlord will promptly undertake such repairs or alterations at its own expense,
not subject to inclusion as Operating Expenses. If any capital improvements or
replacement of capital equipment is necessitated by such interruptions or
malfunctions, the costs of such improvements or replacements shall be borne
solely by Landlord and excluded from Operating Expenses.

     9.   Merger. All negotiations, considerations, representations and
understandings between Landlord and Tenant relating to this Eighth Amendment are
incorporated herein and may be modified or altered only by agreement, in
writing, between Landlord and Tenant. No modification, termination, or surrender
of the Lease, as modified by this Eighth Amendment, or surrender of the Premises
(including the 20th Floor Expansion Space) or any part thereof or of any
interest therein by Tenant shall be valid or effective unless agreed to and
accepted, in writing, by Landlord an no act by any representative or agent of
Landlord other than delivery of such a written agreement and acceptance by
Landlord shall constitute agreement to and acceptance thereof. Any prior
negotiations or intentions of the parties relating to this Eighth Amendment,
whether oral or evidenced by written documentation dated prior to the date of
this Eighth Amendment, are null and void, unless specifically incorporated
herein by reference.

     10.  Exoneration Clause. This Eighth Amendment is executed by the
undersigned, American National Bank and Trust Company of Chicago, not
personally, but as Trustee in the exercise of the power and authority conferred
upon and vested in it as such Trustee and under the express direction of the
beneficiaries of the said Trust. It is expressly understood and agreed that all
of the warranties, indemnities, representations, covenants, undertaking sand
agreements herein made on the part of the Trustee are undertaken by it solely in
its capacity as Trustee and

<PAGE>

not personally. No personal liability or personal responsibility is assumed by
or shall at any time be asserted or enforceable against the Trustee on account
of any warranty, indemnity, representation, covenant, undertaking or agreement
of the Trustee in this instrument.

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


LANDLORD:                            AMERICAN NATIONAL BANK AND TRUST COMPANY OF
                                     CHICAGO, not individually, but solely as
                                     Trustee under Trust Agreement dated April
                                     5, 1990 and known as Trust No. 110513-07


                                     By:  /s/David Rosenfeld
                                        -----------------------------
                                     Title:  Assistant Vice President
                                           --------------------------

                                     Attest: Attestation not required by
                                     American National Bank and Trust Company of
                                     Chicago Bylaws
                                                        ______________ Secretary

                                     THE NORTHERN TRUST COMPANY



                                     By:  /s/Wayne LaChance
                                        -----------------------------
                                     Title:  Vice President
                                           --------------------------
<PAGE>

                                   EXHIBIT A
                                   ---------

                          20TH FLOOR EXPANSION SPACE
                          --------------------------