EXHIBIT 10.15

                                 PROMISSORY NOTE

                                                                Honolulu, Hawaii
$1,000,000.00                                                  February 27, 1997


         FOR VALUE RECEIVED,  CYANOTECH CORPORATION, a Nevada corporation,  (the
"Maker"),  promises  to pay to the  order  of  FIRST  HAWAIIAN  BANK,  a  Hawaii
corporation, at its main office at 999 Bishop Street, Honolulu, Hawaii 96813, or
at such other place as the holder of this Note (the  "Holder")  may from time to
time   designate,   the  principal  sum  of  ONE  MILLION  AND  NO/000   DOLLARS
($1,000,000.00),  or so much thereof as is from time to time advanced,  together
with  interest on each advance of the principal  sum, from the date thereof,  at
the interest rate specified below on the principal balance remaining unpaid from
time to time.

         Interest.  The interest  payable under this Note shall be a fluctuating
rate per  annum  equal to one  (1.0%)  percentage  point  higher  than the Prime
Interest  Rate (as  hereinafter  defined) in effect from time to time during the
term of this Note.  Each  change in such  fluctuating  rate  shall  take  effect
simultaneously with the corresponding change in the Prime Interest Rate. As used
herein,  the term "Prime  Interest Rate" shall mean the lending rate of interest
per annum  announced  publicly by First  Hawaiian  Bank from time to time as its
"Prime  Interest  Rate",  which rate shall not necessarily be the best or lowest
rate  charged  by First  Hawaiian  Bank  from  time to time.  Interest  shall be
computed  on the  basis of a year of 365  days,  and the  actual  number of days
elapsed.

         Payments;  Maturity  Date.  Interest  only shall be payable  monthly in
arrears,  commencing on the last day of February,  1997,  and  continuing on the
last day of each calendar month  thereafter  until the principal and interest on
this Note are fully paid. All unpaid  principal and accrued but unpaid  interest
shall be due and payable on January 31, 1998,  unless sooner due as  hereinafter
provided (the "Maturity Date").

         Application  of  Payments.  Except  in the case of an  election  to the
contrary by the Holder, and to the extent permitted by law, all payments will be
applied first to charges, then interest, then principal.

         Prepayments.  The Maker may make  prepayments  of  principal  without a
prepayment  charge,  but with accrued interest thereon.  Any prepayment shall be
applied  against the  principal sum  outstanding  and shall not postpone the due
date of any  subsequent  monthly  payment or change the amount of any subsequent
monthly payment.

         Default.  If the Maker  shall  default  in the  payment  of  principal,
interest  or other fees or charges  when due under this Note,  or if an Event of
Default,  as defined in that  certain  Credit  Agreement  executed  concurrently
herewith by the Maker,  shall occur (this  Note,  the Credit  Agreement  and all
other  agreements  and  security   instruments  referred  to  therein  as  "Loan
Documents",  being hereinafter  called the "Loan  Documents"),  then, and in any
such event, the Holder shall have the option to declare the unpaid principal sum
of this Note,  together with all interest accrued thereon, and all fees, charges
and  other  sums  payable  under the  Loan  Documents,  including any applicable
prepayment charge, to be immediately due and payable, and such principal sum and
interest, and all such fees, charges and other sums, including any

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applicable  prepayment charge, shall thereupon become and be due and payable
without  presentment,  demand,  protest or notice of any kind,  all of which are
hereby expressly waived, and, upon such maturity,  by acceleration or otherwise,
the unpaid  principal  balance,  all accrued but unpaid  interest,  and all such
fees, charges and other sums, including any applicable  prepayment charge, shall
thereafter  bear interest until fully paid at a rate per annum equal to four (4)
percentage  points  higher than the rate that would  otherwise be in effect from
time to time  under  this  Note.  Failure  to  exercise  this  option  shall not
constitute  a waiver of the right to exercise  the same in the event of the same
or any subsequent default.

         Late Charges.  If any monthly  installment  payment shall not have been
paid within ten (10) days after the same becomes due and payable, the Holder, in
addition to its other remedies,  may collect, and the Maker shall pay on demand,
a late charge equal to five percent (5%) of the amount overdue.

         Reasonableness  of  Default  Charges.   The  Maker   acknowledges  that
nonpayment of any monthly  payment when due and nonpayment at maturity  (whether
or not  resulting  from  acceleration  due to an event of default under the Loan
Documents)  will  result in damages  to the  Holder by reason of the  additional
expenses  incurred in servicing the  indebtedness  evidenced by this Note and by
reason of the loss to the Holder of the use of the money due and  frustration to
the Holder in meeting its other  commitments.  The Maker also  acknowledges  and
agrees  that the  occurrence  of any  other  event  of  default  under  the Loan
Documents will result in damages to the Holder by reason of the detriment caused
thereby.  The  Maker  further  acknowledges  that it is and  will  be  extremely
difficult and  impracticable  to ascertain the extent of such damages  caused by
nonpayment  of any sums when due or  resulting  from any other  event of default
under the Loan Documents.  The Maker by its execution and delivery of this Note,
and the Holder by the  acceptance of this Note agree that a reasonable  estimate
of such  damages must be based in part upon the duration of the default and that
the rate of interest prescribed above with respect to the amount due and payable
after maturity or acceleration  and the late charge specified above with respect
to delinquent  payments  would not  unreasonably  compensate the Holder for such
damages.

         U. S. Money.  Principal and interest  shall be payable  in lawful money
of the United States of America, in immediately available funds.

         Attorneys' Fees. The Maker promises to pay the Holder's attorneys' fees
and such  expenses as are  incurred to induce or compel the payment of this Note
or any portion of the  indebtedness  evidenced  hereby,  whether suit is brought
hereon or not.

         Waiver.  Except as otherwise provided herein, the Maker,  indorsers and
guarantors  hereof and all  others  who may  become  liable for any part of this
obligation severally waive presentment,  protest,  demand and notice of protest,
demand,  dishonor  and  nonpayment  of this Note and  consent  to any  number of
renewals  or  extensions  of the time of payment  hereof  and to any  release of
parties obligated hereunder or forbearance in the enforcement hereof.

         No Oral Waiver, Modification or Cancellation. No provision in this Note
may be waived,  modified or canceled orally, but only by an agreement in writing
and signed by the 
                                       2

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party  against  whom  enforcement  of  any  waiver,  modification, discharge  or
cancellation is sought.

         Governing Law.  This Note shall be governed by  and construed according
to the laws of the State of Hawaii.

         Limitations on Interest.  Notwithstanding any provision to the contrary
contained in the Loan Documents, the rate and amount of interest which the Maker
shall be  required  to pay to the  Holder  shall  in no  event,  contingency  or
circumstance  exceed the maximum rate or amount  limitation,  if any, imposed by
applicable law. If, from any circumstance  whatsoever,  performance by the Maker
of any obligation under the Loan Documents at the time performance  shall be due
(including, without limiting the generality of the foregoing, the payment of any
fee,  charge or expense  paid or incurred by the Maker which shall be held to be
interest),  shall involve transcending the limits of validity prescribed by law,
if any, then, automatically, such obligation to be performed shall be reduced to
the limit of such validity prescribed by applicable law. If, notwithstanding the
foregoing limitations, any excess interest shall at the maturity of this Note be
determined to have been received,  the same shall be deemed to have been held as
additional  security.  The  foregoing  provisions  shall never be  superseded or
waived and shall control  every other  provision of all  agreements  between the
Holder and the Maker.

         IN WITNESS WHEREOF, the Maker has caused this Note to be duly executed.



                                       CYANOTECH CORPORATION

                                                                 "Maker"
                                       By /s/Ronald P. Scott
                                          ------------------
                                          Its Exec. V.P./CEO


                                       By
                                          ------------------
                                          Its
                                                                 "Maker"

WITNESSED:

/s/T. Kelii Leong
------------------
                                       3
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STATE OF HAWAII                          )
                                         )        SS:
COUNTY OF HAWAII                         )



     On this 27th day of February, 1997, personally appeared Ronald P. Scott, to
me personally  known,  who, being by me duly sworn or affirmed did say that such
person(s)  executed the  foregoing  instrument  as the free act and deed of such
person(s), and if applicable, in the capacity shown, having been duly authorized
to execute such instrument in such capacity.
                                                  /s/Lei T. Cabilin
                                                  ------------------------------
                                                  Notary Public, State of Hawaii

                                                  My commission Expires: 7/03/99


<PAGE>
STATE OF HAWAII                          )
                                         )        SS:
COUNTY OF HAWAII                         )



     On this 27th day of February, 1997, personally appeared Ronald P. Scott, to
me personally  known,  who, being by me duly sworn or affirmed did say that such
person(s)  executed the  foregoing  instrument  as the free act and deed of such
person(s), and if applicable, in the capacity shown, having been duly authorized
to execute such instrument in such capacity.
                                                  /s/Lei T. Cabilin
                                                  ------------------------------
                                                  Notary Public, State of Hawaii

                                                  My commission Expires: 7/03/99
<PAGE>



STATE OF HAWAII                          )
                                         ) SS.
COUNTY OF HAWAII                         )


     On this 27th day of February, 1997, personally appeared Ronald P. Scott, to
me personally  known,  who, being by me duly sworn or affirmed did say that such
person(s)  executed the  foregoing  instrument  as the free act and deed of such
person(s), and if applicable, in the capacity shown, having been duly authorized
to execute such instrument in such capacity.
                                                  /s/Lei T. Cabilin
                                                  ------------------------------
                                                  Notary Public, State of Hawaii

                                                  My commission Expires: 7/03/99
<PAGE>
STATE OF HAWAII                          )
                                         ) SS.
COUNTY OF HAWAII                         )


     On this 27th day of February, 1997, personally appeared Ronald P. Scott, to
me personally  known,  who, being by me duly sworn or affirmed did say that such
person(s)  executed the  foregoing  instrument  as the free act and deed of such
person(s), and if applicable, in the capacity shown, having been duly authorized
to execute such instrument in such capacity.

                                                  /s/Lei T. Cabilin
                                                  ------------------------------
                                                  Notary Public, State of Hawaii

                                                  My commission Expires: 7/03/99