<PAGE>
 
                                 EXHIBIT 10.9

                                PROMISSORY NOTE

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<CAPTION>
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  Principal      Loan Date      Maturity      Loan No       Call       Collateral     Account      Officer       Initials
<S>             <C>            <C>            <C>           <C>        <C>            <C>          <C>           <C>   
$2,500,000.00   09-01-1997     09-01-1998     9240904       4A0           9093        9240904       63141
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</TABLE> 
References in the shaded area are for Lender's use only and do not limit the
applicability of this document to any particular loan or item.
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<TABLE> 


<S>        <C>                                    <C>                <C>
Borrower:  Wave Technologies International, Inc.  (TIN: 43-1481443)  Lender:  COMMERCE BANK, N.A.
           10845 Olive Blvd                                                   8000 Forsyth
           St. Louis, MO  63141                                               P.O. Box 11573
                                                                              St. Louis, MO  63105-0373
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</TABLE>

<TABLE>

<S>                <C>             <C>            <C>       <C>            <C>
Principal Amount:  $2,500,000.00   Initial Rate:  8.500%    Date of Note:  September 1, 1997
</TABLE>
PROMISE TO PAY.  Wave Technologies International, Inc. ("Borrower") promises to
pay to COMMERCE BANK, N.A. ("Lender"), or order, in lawful money of the United
States of America, the principal amount of Two Million Five Hundred Thousand &
00/100 Dollars ($2,500,000.00) or so much as may be outstanding, together with
interest on the unpaid outstanding principal balance of each advance. Interest
shall be calculated from the date of each advance until repayment of each
advance.

PAYMENT.  Borrower will pay this loan in one payment of all outstanding
principal plus all accrued unpaid interest on September 1, 1998. In addition,
Borrower will pay regular monthly payments of accrued unpaid interest beginning
October 1, 1997, and all subsequent interest payments are due on the same day of
each month after that. Interest on this Note is computed on a 365/360 simple
interest basis; that is, by applying the ratio of the annual interest rate over
a year of 360 days, multiplied by the outstanding principal balance, multiplied
by the actual number of days the principal balance is outstanding. Borrower will
pay Lender at Lender's address shown above or at such other place as Lender may
designate in writing. Unless otherwise agreed or required by applicable law,
payments will be applied first to accrued unpaid interest, then to principal,
and any remaining amount to any unpaid collection costs and late charges.

VARIABLE INTEREST RATE.  The interest rate on this Note is subject to change
from time to time based on changes in an index which is the per annum rate from
time to time announced by Lender at its main office as the prime rate, or as the
case may be, the base, reference or other rate then in use for commercial loan
reference purposes, not necessarily the lowest or even favored rate, which
serves as the basis upon which effective rates of interest are calculated for
those loans making reference thereto (the "Index"). Lender will tell Borrower
the current Index rate upon Borrower's request. Borrower understands that Lender
may make loans based on other rates as well. The interest rate change will not
occur more often than each Day. Rates of interest tied to the Index shall change
with and be effective on the date of each change in the Index. The Index
currently is 8.500% per annum. The interest rate to be applied to the unpaid
principal balance of this Note will be at a rate equal to the Index, resulting
in an initial rate of 8.500% per annum. NOTICE: Under no circumstances will the
interest rate on this Note be more than the maximum rate allowed by applicable
law.

PREPAYMENT.  Borrower agrees that all loan fees and other prepaid finance
charges are earned fully as of the date of the loan and will not be subject to
refund upon early payment (whether voluntary or as a result of default), except
as otherwise required by law. Except for the foregoing, Borrower may pay without
penalty all or a portion of the amount owed earlier than it is due. Early
payments will not, unless agreed to by Lender in writing, relieve Borrower of
Borrower's obligation to continue to make payments of accrued unpaid interest.
Rather, they will reduce the principal balance due.

DEFAULT.  Borrower will be in default if any of the following happens: (a)
Borrower fails to make any payment when due. (b) Borrower breaks any promise
Borrower has made to Lender, or Borrower fails to comply with or to perform when
due any other term, obligation, covenant, or condition contained in this Note or
any agreement related to this Note, or in any other agreement or loan Borrower
has with Lender. (c) Any representation or statement made or furnished to Lender
by Borrower or on Borrower's behalf is false or misleading in any material
respect either now or at the time made or furnished. (d) Borrower becomes
insolvent, a receiver is appointed for any part of Borrower's property, Borrower
makes an assignment for the benefit of creditors, or any proceeding is commenced
either by Borrower or against Borrower under any bankruptcy or insolvency laws.
(e) Any creditor tries to take any of Borrower's property on or in which Lender
has a lien or security interest. This includes a garnishment of any of
Borrower's accounts with Lender. (f) Any guarantor dies or any of the other
events described in this default section occurs with respect to any guarantor of
this Note or any guarantor seeks, claims or otherwise attempts to limit, modify
or revoke such guarantor's guarantee of this Note. (g) A material adverse change
occurs in Borrower's financial condition, or Lender believes the prospect of
payment or performance of the Indebtedness is impaired. (h) Lender in good faith
deems itself insecure.

LENDER'S RIGHTS.  Upon default, Lender may declare the entire unpaid principal
balance on this Note and all accrued unpaid interest immediately due, without
notice, and then Borrower will pay that amount. Upon default, including failure
to pay upon final maturity, Lender, at its option, may also, if permitted under
applicable law, do one or both of the following: (a) increase the variable
interest rate on this Note to 3.000 percentage points over the index, and (b)
add any unpaid accrued interest to principal and such sum will bear interest
therefrom until paid at the rate provided in this Note (including any increased
rate).  The interest rate will not exceed the maximum rate permitted by
applicable law. Lender may hire or pay someone else to help collect this Note if
Borrower does not pay. Borrower also will pay Lender that amount. This includes,
subject to any limits under applicable law, Lender's attorneys' fees and
Lender's legal expenses whether or not there is a lawsuit, including attorneys'
fees and legal expenses for bankruptcy proceedings (including efforts to modify
or vacate any automatic stay or injunction), appeals, and any anticipated post-
judgment collection services. If not prohibited by applicable law, Borrower also
will pay any court costs, in addition to all other sums provided by law. This
Note has been delivered to Lender and accepted by Lender in the State of
Missouri. If there is a lawsuit, Borrower agrees upon Lender's request to submit
to the jurisdiction of the courts of St. Louis County, the State of Missouri.
Lender and Borrower hereby waive the right to any jury trial in any action,
proceeding, or counterclaim brought by either Lender or Borrower against the
other. This Note shall be governed by and construed in accordance with the laws
of the State of Missouri.

RIGHT OF SETOFF.  Borrower grants to Lender a contractual possessory security
interest in, and hereby assigns, conveys, delivers, pledges, and transfers to
Lender all Borrower's right, title and interest in and to, Borrower's accounts
with Lender (whether checking, savings, or some other account), including
without limitation all accounts held jointly with someone else and all accounts
Borrower may open in the future, excluding however all IRA and Keogh accounts,
and all trust accounts for which the grant of a security interest would be
prohibited by law. Borrower authorizes Lender, to the extent permitted by
applicable law, to charge or setoff all sums owing on this Note against any and
all such accounts.

LINE OF CREDIT.  This Note evidences a revolving line of credit.  Advances under
this Note may be requested orally by Borrower or by an authorized person.
Lender may, but need not, require that all oral requests be confirmed in
writing.  All communications, instructions, or directions by telephone or
otherwise to Lender are to be directed to Lender's office shown above.  The
following party or parties are authorized to request advances under the line of
credit until Lender receives from Borrower at Lender's address shown above
written notice of revocation of their authority:  Kenneth W Kousky, President;
J. M. Bowles, CFO; and Douglas A Wilmsmeyer, Vice President.  Borrower agrees to
be liable for all sums either: (a) advanced in accordance with the instructions
of an authorized person or (b) credited to any of Borrower's accounts with
Lender. The unpaid principal balance owing on this Note at any time may be
evidenced by endorsements on this Note or by Lender's internal records,
including daily computer print-outs. Lender will have no obligation to advance
funds under this Note if: (a) Borrower or any guarantor is in default under the
terms of this Note or any agreement that Borrower or any guarantor has with
Lender, including any agreement made in connection with the signing of this
Note; (b) Borrower or any guarantor ceases doing business or is insolvent; (c)
any guarantor seeks, claims or otherwise attempts to limit, modify or revoke
such guarantor's guarantee of this Note or any other loan with Lender; (d)
Borrower has applied funds provided pursuant to this Note for purposes other
than those authorized by Lender; or (e) Lender in good faith deems itself
insecure under this Note or any other agreement between Lender and Borrower.

PRIOR NOTE.  "This is a renewal of Borrower's note dated September 1, 1996."
ALSO: This Note is subject to the terms and conditions of the General Loan and
Security Agreement dated August 31, 1995, and amended January 5, 1996 and
September 1, 1996.

GENERAL PROVISIONS.  Lender may delay or forgo enforcing any of its rights or
remedies under this Note without losing them.  Borrower and any other person who
signs, guarantees or endorses this Note, to the extent allowed by law, waive
presentment, demand for payment, protest and notice of dishonor.  Upon any
change in the terms of this Note, and unless otherwise expressly stated in
writing, no party who signs this Note, whether as maker, guarantor,
accommodation maker or endorser, shall be released from liability.  All such
parties agree that Lender may renew or extend (repeatedly and for any length of
time) this loan, or release any party or guarantor or collateral; or impair,
fail to realize upon or perfect Lender's security interest in the collateral;
and take any other action deemed necessary by Lender without the consent of or
notice to anyone.  All such parties also agree that Lender may modify this loan
without the consent of or notice to anyone other than the party with whom the
modification is made.
<PAGE>
                            PROMISSORY NOTE                               Page 2
09-01-1997                   (Continued)
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PRIOR TO SIGNING THIS NOTE, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS OF
THIS NOTE, INCLUDING THE VARIABLE INTEREST RATE PROVISIONS.  BORROWER AGREES TO
THE TERMS OF THE NOTE AND ACKNOWLEDGES RECEIPT OF A COMPLETED COPY OF THE NOTE.

ORAL AGREEMENTS OR COMMITMENTS TO LOAN MONEY, EXTEND CREDIT OR TO FOREBEAR FROM
ENFORCING REPAYMENT OF A DEBT INCLUDING PROMISES TO EXTEND OR RENEW SUCH DEBT
ARE NOT ENFORCEABLE. TO PROTECT YOU (BORROWER(S)) AND US (CREDITOR) FROM
MISUNDERSTANDING OR DISAPPOINTMENT, ANY AGREEMENTS WE REACH COVERING SUCH
MATTERS ARE CONTAINED IN THIS WRITING, WHICH IS THE COMPLETE AND EXCLUSIVE
STATEMENT OF THE AGREEMENT BETWEEN US, EXCEPT AS WE MAY LATER AGREE IN WRITING
TO MODIFY IT.

BORROWER:

Wave Technologies International, Inc.

x /s/ J. M. Bowles
-----------------------------------------------
    Authorized Officer

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