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                                                                   EXHIBIT 10.17

                          SINGLE PRINCIPAL PAYMENT NOTE



U.S. $200,000                                                   December 1, 1999
                                                                Phoenix, Arizona


                  FOR VALUE RECEIVED, Lou L. Ross ("Borrower"), hereby promises
to pay to the order of National Scientific Corporation, a Texas corporation
("Lender"), the principal amount of $200,000, together with interest on the
principal balance outstanding hereunder, from (and including) the date of
disbursement until (but not including) the date of payment, at a per annum rate
equal to the Stated Interest Rate specified below, in accordance with the
following terms and conditions:

         1. STATED INTEREST RATE. The principal balance outstanding hereunder
from time to time shall bear interest at 9% per annum, calculated daily on the
basis of actual days elapsed over a 360-day year.

         2. MATURITY. The principal balance outstanding hereunder, together with
all accrued interest and other amounts payable hereunder, if not sooner paid as
provided herein, shall be due and payable December 1, 2000. Lender may extend
the time for payment of or renew this Note, or release any party from liability
hereunder, and any such extension, renewal, release or other indulgence shall
not alter or diminish the liability of Borrower or any other person or entity
who is or may become liable on this Note.

         3. EVENTS OF DEFAULT; ACCELERATION. The occurrence of any one or more
of the following events shall constitute an "Event of Default" hereunder, and
upon such Event of Default, the entire principal balance outstanding hereunder,
together with all accrued interest and other amounts payable hereunder, at the
election of Lender, shall become immediately due and payable, without any notice
to Borrower:

                  (a) Nonpayment of principal, interest or other amounts when
the same shall become due and payable hereunder; or

                  (b) The failure of Borrower to comply with any provision of
this Note.

         4. WAIVERS. Except as set forth in this Note, to the extent permitted
by applicable law, Borrower, and each person who is or may become liable
hereunder, severally waive and agree not to assert: (a) any homestead or
exemption rights; (b) demand, diligence, grace, presentment for payment,
protest, notice of nonpayment, nonperformance, extension, dishonor, maturity,
protest and default; and (c) recourse to guaranty or suretyship defenses
(including, without limitation, the right to require the Lender to bring an
action on this Note).

         5. NO WAIVER BY LENDER. No delay or failure of Lender in exercising any
right hereunder shall affect such right, nor shall any single or partial
exercise of any right preclude further exercise thereof.
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         6. GOVERNING LAW. This Note shall be construed in accordance with and
governed by the laws of the State of Arizona, without regard to the choice of
law rules of the State of Arizona.

         7. AMENDMENTS. No amendment, modification, change, waiver, release or
discharge hereof and hereunder shall be effective unless evidenced by an
instrument in writing and signed by the party against whom enforcement is
sought.

         8. SEVERABILITY. If any provision hereof is invalid or unenforceable,
the other provisions hereof shall remain in full force and effect and shall be
liberally construed in favor of Lender in order to effectuate the other
provisions hereof.

         IN WITNESS WHEREOF, Borrower has executed this Note as of the date
first set forth above.

                                                  "BORROWER"



                                                            /s/ L. L. Ross
                                                  -----------------------------
                                                  Lou L. Ross



                                                  Address of Borrower:



                                                  2243 North Lemon St.
                                                  -----------------------------



                                                  Mesa, Arizona 85215
                                                  -----------------------------



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