EXHIBIT 10.8(a)

SECOND AMENDMENT OF LEASE

            PlyProperties, a partnership (“Lessor”) and TheraSense, Inc., a
Delaware corporation (“Lessee”) entered into a lease (the “Lease”) dated
February 26, 1999, and later amended, covering property at 1360–1380 South Loop
Road, Alameda, California (the “Property”).

            Pursuant to paragraph 55 of the Lease, Lessee has exercised its
option to expand the leased Premises (“Phase II”), and the parties wish to amend
said Lease to provide for and cover said expansion.

            1.   Construction of Phase II Improvements. Lessor agrees, in
accordance with the attached Work Letter (“Exhibit B-2”), at its sole cost and
expense except as provided for below, and as soon as it can reasonably be
accomplished following the execution of this Lease, to (1) complete and submit
plans and specifications covering the Phase II expansion to Lessee for its
approval (for all intent and purposes and for their mutual benefit Lessor and
Lessee have worked together with the architects and engineers in preparing said
plans and specifications), which approval shall not be unreasonably withheld,
said Phase II building and improvements to be in conformity with JWD’s plans and
specifications (Project No. D01003), dated March 29, 2002, a copy of which is
attached hereto and made a part hereof; (2) apply for and secure appropriate
building permits; (3) secure construction financing; and (3) commence and
prosecute to completion in a diligent and good and workmanlike manner the
construction and delivery of said Phase II building and improvements to Lessee.
The parties hereto are aiming toward the substantial completion and delivery of
Phase II to Lessee by April 1, 2003, provided Lessor is not delayed by causes
beyond its control, which shall include but not be limited to any unanticipated
delays in securing permits and/or financing; delays in construction due to
fires, unusually severe weather, labor problems, including strikes or slowdowns;
acts of God, and other similar causes; change orders; and delays caused by the
Lessee or its agents and/or sub-contractors.

Should Lessor fail to deliver the Premises by the above projected date, then
this Second Amendment of Lease shall be effective upon the date Lessor does
substantially complete the above work, as previously defined in the Lease, and
delivers possession thereof to Lessee.

If the actual commencement date of this Lease is other than that set forth in
paragraph 2 below, then Lessor and Lessee shall prepare and execute a further
amendment of lease setting forth the revised commencement date(s) of the Lease
term, but failure to execute such an amendment shall not affect the actual
commencement date(s).

            2.   Lease Terms. Commencing upon the substantial completion and
delivery of the Phase II improvements, the term of this Lease (covering both the
Phase I and II buildings and improvements) shall be extended out to a new ten
(10) year term. For example:

                  a.  If the Phase II improvements are completed and delivered,
as projected, on April 1, 2003, then the Phase II portion of the Lease shall
commence on April 1, 2003 and end March 31, 2013, subject to any extensions as
provided for below; and

                  b.  Based on those same dates, the term for the existing,
Phase I portion of the Lease shall be extended from its current August 14, 2009
expiration date to also terminate on the above March 31, 2013 date, again
subject to any extensions as provided for below.

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                   c. Lessee’s right of prior termination, as provided for in
paragraph 1.3 of the Rider To Lease, is hereby cancelled.

             3.   Rental.

                   a. Phase II. Lessee’s additional base monthly triple net
rent, as defined in the Lease, for the Phase II building and improvements shall
equal $82,750.00 ($1.30/SF) per month, beginning on the commencement date of the
Phase II lease as established above, and subject to any increases brought about
by approved change orders to the aforementioned plans and specifications, and/or
future rent adjustments, as set forth below.

                   b. Phase I. Lessee’s base monthly triple net rent for the
Phase I building and improvements shall continue the same as currently set forth
in the Lease until adjusted as set forth below.

                   c. Rental Adjustments applicable to Phase II. The above
triple net base rent shall be adjusted every two and one-half years during the
Phase II portion of the lease as follows:

                      (1) Months 31 through 60: The above initial base monthly
rent shall be adjusted at the beginning of the 31st month, and the base rent as
so adjusted shall be payable each succeeding month until the end of the 60th
month, as follows: The base for computing the adjustment is the Consumer Price
Index for All Urban Consumers, San Francisco-Oakland, published by the United
States Department of Labor, Bureau of Labor Statistics (“Index”), which is
published for the month of January, 2003 (“Beginning Index”). If the Index
published for the month of July immediately preceding the 31st month adjustment
date (“31st Month Adjustment Index”) is increased over the Beginning Index, the
base monthly rent payable for each month of the term commencing with the 31st
month, and continuing through the 60th month, shall be set by multiplying the
initial or original base rent by a fraction, the numerator of which is the 31st
Month Adjustment Index and the denominator of which is the Beginning Index.

Notwithstanding the foregoing, in no event shall the base rent be increased
pursuant to this paragraph by less than five (5%) percent every two and one-half
years (2% per year, non-compounded), or greater than seven and one-half (7.5%)
percent every two and one-half years (3% per year, non-compounded).

                      (2) Months 61 through 90; and 91 through 120: To be
adjusted based on the same formula or method described above.

                      (3) If the Index is changed so that the base year differs
from 1982-84 = 100, the Index shall be converted in accordance with the
conversion factor published by the United States Department of Labor, Bureau of
Labor Statistics. If the Index is discontinued or otherwise revised during the
Lease term, such other governmental Index or computation with which it is
replaced will be used in order to obtain substantially the same result as would
be obtained if the Index would not have been revised or discontinued.

                   d. Rent Adjustments applicable to Phase I. Said adjustments
applicable to the Phase I rent, as set forth in paragraph 50.d. of the Lease,
shall continue on schedule (i.e. adjusted every two and one-half years of the
Phase I portion of the Lease), beginning August 15, 1999.

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             4. Cost Overruns. Notwithstanding any provision of this Lease to
the contrary, it is understood and agreed that Lessee shall pay to Lessor in
cash, within thirty (30) days after Lessor delivers possession of the Phase II
Premises to Lessee, or within thirty (30) days of the construction and payment
by Lessor of any work specifically ordered by Lessee that is outside of the
scope of Lessor’s work set forth in Exhibit “B-2” to this Lease, any
construction costs paid or incurred by Lessor in excess of the tenant
improvement (“T.I.”) allowance of $25 per square foot that is provided for in
Exhibit “B-2”.

Lessee shall have the right to increase the above T.I. allowance of $25 per
square foot to $29 per square foot by increasing the rent due for Phase II by an
amount so as to amortize said additional $4.00 per square foot of costs over the
ten (10) year term of the Phase II portion of the Lease at eleven (11%) per
annum interest.

Prior to the start of major tenant improvement work, Lessor will provide Lessee
with budget estimates for the work described in paragraph 1 above. Such
estimates shall represent Lessor’s reasonable estimates based on contractor
estimates or information then known by Lessor, but Lessee agrees that such
estimates are subject to change based upon (i) change in design; (ii) time;
(iii) actual bids received; (iv) delays in construction; or (v) other reasonable
changes or adjustments. Lessor makes no representation that the budget estimates
will equal the actual costs incurred. Lessor will reasonably advise Lessee from
time to time as to material changes in the budget or actual costs.

             5. Brokers. Each party represents that it has not had dealings with
any real estate company, broker, agent, finder, or other person with respect to
this Phase II portion of the Lease in any manner, except for the Donald L. Jones
Company. Each party shall hold harmless the other party from all damages
resulting from any claims that may be asserted against the other party by any
broker, agent, finder, or other person with whom such indemnifying party has or
purportedly has dealt.

             6. Option to Renew. Effective as of the expiration date of this
extended Lease term, Lessor grants to Lessee an option to renew this Lease for
an additional five (5) year period on the same terms, conditions, covenants,
agreements or amendments, if any, then in force pursuant to this Lease except
for the amount of the rental which shall be determined either by agreement
between the parties or by arbitration based on the fair market rent value of the
Premises. For the purposes of this clause, fair market rent shall be defined as
the probable triple net rent that the Premises should bring in a competitive and
open market at the time that this option is exercised, with the landlord and a
“highest and best use” tenant acting prudently and knowledgeably, based on the
“as is” condition of the Premises at that time and upon lease terms and
conditions consistent with those that govern this Lease extension.

If Lessor and Lessee are unable to agree upon said fair market rent value within
thirty (30) days from notice of exercise of the option herein granted, then it
will be set either by a qualified MAI appraiser chosen by the parties, or by
arbitration as follows:

             a. Within five (5) days after written notice by either party to the
other requesting arbitration, one arbitrator shall be appointed by each party.
Notice in writing of such appointment, when made, shall be given by each party
to the other. The two arbitrators so named shall meet promptly and seek to reach
a conclusion as to the fair market rent value of the Premises, and their
decision rendered in writing and delivered to the parties hereto shall be final
and binding on the parties.

             b. If said two (2) arbitrators shall fail to reach a decision
within fifteen (15) days after appointment of the second arbitrator, then the
two arbitrators shall forthwith choose a third arbitrator

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within five (5) days to act with them. If they fail to select a third arbitrator
within said five (5) days, the third arbitrator shall be promptly appointed by
the Presiding Judge of the Superior Court, State of California, County of
Alameda. The party making such application to said Judge shall give the other
party hereto five (5) days written notice thereof.

                 c. The arbitration shall proceed with due dispatch. The third
arbitrator shall select the value submitted by one of the initial two
arbitrators that is closest to the value determined by the third arbitrator. The
decision of third arbitrator, reached accordingly, shall be binding, final and
conclusive on the parties hereto. Such decision shall be in writing and
delivered to the parties.

                 d. If either party fails to appoint an arbitrator as herein
provided, then the arbitrator that has been appointed shall be the sole
arbitrator.

                 e. The expense of any such arbitration shall be borne equally
between the parties hereto, except that the cost of any attorney’s fees incurred
by the parties are their own respective responsibilities.

                 f. The arbitration shall be conducted in accordance with the
applicable statutes of the State of California then in effect.

                 g. All arbitrators selected shall be licensed real estate
brokers with not less than 10 years experience dealing with commercial
properties similar to the Property in the same general area as the Property.

Lessee shall exercise this option by serving written notice upon Lessor of its
intent to exercise the option at least six (6) months prior to the expiration of
the extended ten year term of this Lease. Lessee shall have the right to
exercise this option only in the event that Lessee is not in default in its
performance of any material term or condition of the Lease.

             7. Expansion. The parties wish to anticipate the possible further
expansion of the Premises (“Phase III”) as generally shown on the Master Plan
for the site. Upon delivery of written notice (the “Expansion Notice II”) from
Lessee to Lessor describing the desired expansion (the “Phase III” building and
improvements) and provided that (i) Lessee at Lessor’s reasonable discretion is
financially sound enough to warrant the increased liability and/or risk of the
expanded building and is not in default under any of the terms and conditions
contained herein, (ii) Lessor is able to obtain reasonable third-party financing
for the construction of Phase III, (iii) Phase III is generally in conformance
with the Master Plan for the site; and (iv) building permits and all other
necessary permits or approvals can be reasonably obtained, then Lessor shall
endeavor to develop Phase III.

The rent and terms for Phase III and/or the modification at that time of the
Lease in general, shall be negotiated between the parties based on fair market
conditions, or arbitrated similar to the provisions for arbitration set forth
above; and shall take into consideration, but shall not be limited to, the
number of years remaining on the Lease or any extension thereof, the cost of
third-party financing, the financial strength of the Lessee at the time, the
cost of construction, and the special or general nature of the improvements.

             8. Security Deposit. Lessee’s existing security deposit in the
amount of $500,000 shall remain in place as additional security to the Lessor
and lender or lenders on both the Phase I and II real estate for the term of
this Lease under the conditions previously agreed to except term.

             9. Right of First Purchase. In the event that at any time either
the Lessor or any successor (the

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“Offeror”) wishes to sell the subject real property (“Property”), it shall first
notify Lessee of such intent by written notice (“Notice of Intent”), which
notice shall state the terms and conditions upon which the Offeror intends to
sell or offer the Property.

Thereafter, Lessee shall have the right for a period of fifteen (15) days after
receipt of such written notice to notify the Offeror in writing of its desire to
purchase the Property. Thereafter, the parties shall negotiate the terms and
conditions of such purchase and sale in good faith for a period of up to
forty-five (45) days; provided that the Lessee may in all events during the 45
day period accept the Offeror’s offer as set forth in the Notice of Intent. In
the event the parties reach agreement on such terms and conditions, the purchase
shall be consummated within sixty (60) days after agreement as to the terms and
conditions, or within such other time period as may be agreed to in writing by
the parties.

In the event the parties are unable to reach agreement as to such terms and
conditions, or if the Lessee fails to consummate the purchase of the interests
within the required time period, the Offeror shall have the right to sell the
Property to any third party on terms and conditions that are not substantially
less favorable to Offeror nor better for the buyer than the terms last discussed
and agreed to between the parties, and submitted to writing, for a period of one
hundred eighty (180) days after the expiration of said forty-five (45) day
period. Should Offeror not so sell the Property, or enter into a contract for
such sale within such one hundred eighty (180) day period, then, if Offeror
thereafter desires to sell the Property it shall re-offer the Property to Lessee
as provided herein.

             10. Except as herein specified, all of the other terms and
conditions of the subject Lease shall remain in full force and effect applicable
to both Phase I and Phase II, as appropriate.

             IN WITNESS THEREOF, Lessor and Lessee have executed this Second
Amendment of Lease, this 7th day of May, 2002.

LESSOR     LESSEE             PlyProperties   TheraSense, Inc.                  
  By: /s/ DONALD L. JONES                               By: /s/ W. MARK
LORTZ                                            Donald L. Jones, Managing
Partner     W. Mark Lortz, President & CEO                           By: /s/
CHARLES T. LIAMOS                                          Charles T. Liamos,
Chief Financial Officer