Exhibit 10.1

May 14, 1999

To the Holder of the Series C Senior Convertible Preferred Stock of NaPro
BioTherapeutics, Inc.

Gentlemen:

        Reference is made to (i) the Subscription Agreement (the "Subscription
Agreement"), dated as of December 8, 1997 by and between NaPro BioTherapeutics,
Inc., a Delaware corporation (the "Company" or the "Corporation"), and Advantage
Fund II, Ltd. (the "Holder"); (ii) the Certificate of Designations of Series C
Senior Convertible Preferred Stock (the "Certificate"); (iii) the Amendment
Agreement dated January 28, 1998, by and between the Company and the Holder (the
"January Amendment"); (iv) the Letter Agreement, dated March 31, 1998, by and
between the Company and the Holder (the "March Amendment"); (v) the Letter
Agreement, dated January 7, 1999, by and between the Company and the Holder (the
"January 1999 Amendment"); and (vi) the Letter Agreement, dated March 24, 1999,
by and between the Company and the Holder (the "March 1999 Amendment").
Capitalized terms used herein and not defined shall have the meanings assigned
to them in the Subscription Agreement and the Certificate, as modified by the
January, March, January 1999, and March 1999 Amendments.

        The Holder and the Company agree as follows:

     1. The following definitions in Section 1 of the January 1999 Amendment, as
amended by the March 1999 Amendment, are hereby amended and restated to read as
follows:

        "Initial Redemption Notice Period" means the period that begins on
January 1, 1999 and ends on May 31, 1999.

        "Middle Redemption Amount" means a number of shares of Series C
Preferred Stock equal to 2, 051 less the sum of (x) the aggregate number of
shares of Series C Preferred Stock that are converted by holders of shares of
Series C Preferred Stock or for which the holders of shares of Series C
Preferred Stock give Conversion Notices on or after January 1, 1999 and prior to
May 31, 1999 plus (y) the aggregate number of shares of Series C Preferred Stock
that have been redeemed or called for redemption on or after January 1, 1999 and
prior to the date the Company gives a particular Redemption Notice to redeem
shares of Series C Preferred Stock pursuant to Section 9(a)(5) (together with
accrued and unpaid dividends and Arrearage Interest, if any, on the shares of
Series C Preferred Stock included in the Middle Redemption Amount to the date of
determination).
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        "Middle Redemption Notice Period" means the period that begins on June
1, 1999 and ends on June 30, 1999.

     2. Paragraph (iv) of Section 10(c) of the Certificate, which was deemed to
have been added to Section 10 of the Certificate in accordance with Paragraph 7
of the January 1999 Amendment and was amended in the March 1999 Amendment, is
hereby further amended and restated to read as follows:

        (iv) Notwithstanding any other provision herein, during the period
beginning on January 1, 1999 and ending on May 31, 1999, a holder of shares of
Series C Preferred Stock shall not be entitled to convert shares of Series C
Preferred Stock at a Conversion Price that is less than $4.00 if such conversion
would result in the aggregate number of shares of Common Stock issued hereunder
(whether through conversion or in payment of dividends or otherwise) at a
Conversion Price (or Computed Price, in the case of shares issued as dividends)
of less than $4.00 during the calendar month of the proposed conversion for
which the determination under this paragraph (iv) is being made exceeding
150,000 shares of Common Stock. The Conversion Price set forth in this Section
10(c)(vi) shall be subject to adjustment on the same basis set forth in the
parenthetical phrase in clause (1) of the definition of the term Conversion
Price (as in effect prior to the January Amendment) for any such events that
occur on or after December 31, 1998.

        3. Except as specifically amended or deemed amended hereby, the
Subscription Agreement, as previously amended, and the terms of the shares of
Series C Preferred Stock shall remain in full force and effect and the Company
hereby confirms to the Holder that the Subscription Agreement and the terms of
the shares of Series C Preferred Stock, as deemed amended by the January
Amendment, the March Amendment, the January 1999 Amendment, the March 1999
Amendment and this Agreement, remain binding obligations of the Company that are
not at the time of execution and delivery of this Agreement subject to any
defense, offset, counterclaim or other claim by the Company of invalidity or
unenforceability. If the foregoing correctly sets forth our agreement, please so
indicate by signing the appropriate line below, whereupon this letter shall
constitute a binding agreement between the Company and the Holder under the laws
of the State of New York.

                                                NAPRO BIOTHERAPEUTICS, INC.

                                                By: /s/ Gordon H. Link, Jr.
                                                ---------------------------
                                                Gordon H. Link, Jr.
                                                Chief Financial Officer

Accepted and agreed:

ADVANTAGE FUND II, LTD.


By:  /s/ Declan Quilligan
    ---------------------------
Name: Declan Quilligan
Title:Partner