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                                                                   Exhibit 10.23


                                                           Loan No. 1910185-0001

HELLER FINANCIAL

                                 PROMISSORY NOTE

$4,000,000.00                                                  December 22, 1998

     FOR VALUE RECEIVED, Microcide Pharmaceuticals, Inc., a Delaware corporation
("Maker"), promises to pay to the order of Heller Financial Leasing, Inc., a
Delaware corporation (together with any holder of this Note, "Payee"), at its
office located at 500 West Monroe Street, Chicago, Illinois 60661, or at such
other place as Payee may from time to time designate, the principal sum of Four
Million and 00/100 Dollars ($4,000,000.00), together with interest thereon at a
fixed rate equal to 9 and 55/100 percent (9.55%) per annum. Principal and
interest shall be payable in thirty-six (36) consecutive monthly installments
commencing February 1, 1999, and continuing on the same day of each consecutive
calendar month thereafter until this Note is fully paid, each such installment
in the amount of One Hundred Twenty-eight Thousand Two Hundred Twenty-five and
31/100 Dollars ($128,225.31) provided, however, that in any and all events the
final installment payment hereunder shall be in the amount of the entire then
outstanding principal balance hereunder, plus all accrued and unpaid interest,
charges and other amounts owing hereunder or under the Security Agreement
(defined below). All payments shall be applied first to interest and then to
principal. Interest shall be computed on the basis of a 360 day year comprised
of 30-day months. Maker shall make an interest only initial payment on January
1, 1999 of accrued interest from the loan disbursement date through December 31,
1998.

     Notwithstanding the foregoing, if at any time implementation of any
provision hereof shall cause the interest contracted for or charged herein or
collectable hereunder to exceed the applicable lawful maximum rate, then the
interest shall be limited to such applicable lawful maximum.

     This Note is secured by the collateral described in the Security Agreement
dated December 22, 1998, between Maker and Payee (the "Security Agreement;" and
together with all related documents and instruments, the "Loan Documents") to
which reference is made for a statement of the nature and extent of protection
and security afforded, certain rights of Payee and certain rights and
obligations of Maker, including Maker's rights, if any, to prepay the principal
balance hereof; provided, however, that in addition to any other sum payable
hereunder, under the Security Agreement or any of the other Loan Documents, in
the event of a prepayment of the principal balance hereunder, whether voluntary,
following acceleration or otherwise, Maker shall pay to Payee together with such
prepayment, as liquidated damages to Payee for the loss of its bargain and not
as a penalty, the greater of (i) a sum equal to one percent (1%) of the
principal balance prepaid for each full or partial twelve (12) month period by
which the date of the prepayment precedes the scheduled date of the final
installment of principal under the Note and (ii) a Breakage Fee (defined below).
As used herein, the term "Breakage Fee" shall mean the amount, if any, by which
(A) the present value, in the aggregate, of the then remaining installments of
principal and interest due hereunder, absent the prepayment, using a discount
rate equal to (i) the yield to maturity as of the date two (2) days prior to the
date of the prepayment on United States Treasury securities with a final
maturity approximately equal to the remaining term hereof, absent the
prepayment, as published in The Wall Street Journal, plus (ii) three percent
(3.00%), exceeds (B) the then outstanding principal balance hereunder, absent
the prepayment.

     Time is of the essence hereof. If payment of any installment or any other
sum due under this Note or the Loan Documents is not paid when due, Maker agrees
to pay a late charge equal to the lesser of (i) three cents (3 cents) per dollar
on, and in addition to, the amount of each such payment, or (ii) the maximum
amount Payee is permitted to charge by law. In the event of the occurrence of an
Event of Default (as defined in the Security Agreement), then the entire unpaid
principal balance hereof with accrued and unpaid interest thereon, together with
all other sums payable under this Note or the Loan Documents, shall, at the
option of Payee and without notice or demand, become immediately due and
payable, such accelerated balance bearing interest until paid at the rate of
three and 00/100 percent (3%) per annum above the fixed rate set forth in the
first paragraph of this Note.

     Maker and all endorsers, guarantors or any others who may at any time
become liable for the payment hereof hereby consent to any and all extensions of
time, renewals, waivers and modifications of, and substitutions or release of
security or of any party primarily or secondarily liable on, or with respect to,
this Note or any of the Loan Documents or any of the terms and provisions
thereof that may be made, granted or consented to by Payee, and agree that suit
may be brought and maintained against any one or more of them, at the election
of Payee, without
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joiner of the others as parties thereto, and that Payee shall not be required to
first foreclose, proceed against, or exhaust any security herefor, in order to
enforce payment of this Note by any one or more of them. Maker and all
endorsers, guarantors or any others who may at any time become liable for the
payment hereof hereby severally waive presentment, demand for payment, notice of
nonpayment, protest, notice of protest, notice of dishonor, and all other
notices in connection with this Note, filing of suit and diligence in collecting
this Note or enforcing any of the security herefor, and, without limiting any
provision of any of the Loan Documents, agree to pay, if permitted by law, all
expenses incurred in collection, including reasonable attorneys' fees, and
hereby waive all benefits of valuation, appraisement and exemption laws.

     If there be more than one Maker, all the obligations, promises, agreements
and covenants of Maker under this Note are joint and several.

     THIS NOTE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
INTERNAL LAWS AND DECISIONS OF THE STATE OF ILLINOIS WITHOUT REGARD TO
PRINCIPLES OF CONFLICTS OF LAW. AT PAYEE'S ELECTION AND WITHOUT LIMITING PAYEE'S
RIGHT TO COMMENCE AN ACTION IN ANY OTHER JURISDICTION, MAKER HEREBY SUBMITS TO
THE EXCLUSIVE JURISDICTION AND VENUE OF ANY COURT (FEDERAL, STATE OR LOCAL)
HAVING SITUS WITHIN THE STATE OF ILLINOIS, EXPRESSLY WAIVES PERSONAL SERVICE OF
PROCESS AND CONSENTS TO SERVICE BY CERTIFIED MAIL, POSTAGE PREPAID, DIRECTED TO
THE LAST KNOWN ADDRESS OF MAKER, WHICH SERVICE SHALL BE DEEMED COMPLETED WITHIN
TEN (10) DAYS AFTER THE DATE OF MAILING THEREOF.

     MAKER HEREBY WAIVES ITS RIGHTS TO A JURY TRIAL OF ANY CLAIM OR CAUSE OF
ACTION BASED UPON OR ARISING OUT OF THIS NOTE. THIS WAIVER IS INFORMED AND
FREELY MADE. MAKER ACKNOWLEDGES THAT THIS WAIVER IS A MATERIAL INDUCEMENT TO
ENTER INTO A BUSINESS RELATIONSHIP, THAT PAYEE HAS ALREADY RELIED ON THE WAIVER
IN MAKING THE LOAN EVIDENCED BY THIS NOTE, AND THAT PAYEE WILL CONTINUE TO RELY
ON THE WAIVER IN ITS RELATED FUTURE DEALINGS. MAKER FURTHER WARRANTS AND
REPRESENTS THAT IT HAS REVIEWED THIS WAIVER WITH ITS LEGAL COUNSEL AND THAT IT
KNOWINGLY AND VOLUNTARILY WAIVES ITS JURY TRIAL RIGHTS FOLLOWING CONSULTATION
WITH LEGAL COUNSEL.

Witness/Attest:                             MICROCIDE PHARMACEUTICALS, INC.

By: /S/ Velma Laconsay                      By: /S/  Matthew  J. Hogan
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Controller                                  Chief Financial Officer