Document:

<PAGE>

                                                                   Exhibit 10.11

                       AMENDMENT TO EMPLOYMENT AGREEMENT
                       ---------------------------------

     THIS AMENDMENT TO EMPLOYMENT AGREEMENT ("Amendment") is made this 1/st/ day
of April, 2001, by and between AMERIPATH, INC., a Delaware corporation (the
"Company") and JAMES BILLINGTON (the "Executive").

                              W I T N E S S E T H

     WHEREAS, the Company and the Executive entered into an Employment Agreement
on November 30, 2000 (the "Agreement"); and

     WHEREAS, the Company and the Executive wish to amend the Agreement.

     NOW, THEREFORE, in consideration of the Executive's continued employment
with the Company and other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the Company and the Executive agree
as follows.

     1.  Recitals. The foregoing recitals are true and correct and are
         --------
incorporated herein by this reference.

     2.  Vesting of Options Upon and After Change in Control. Insert the
         ---------------------------------------------------
following at the end of the first sentence in Subsection 5.6 a. of the
Agreement: "and accelerate the vesting of all AmeriPath Stock Options which have
been granted to the Executive, so that the unvested shares are one hundred (100)
percent vested." Insert the following at the end of the second sentence in
Subsection 5.6 a. of the Agreement: "and (5) accelerate the vesting of all
AmeriPath Stock Options which have been granted to the Executive since the
Change in Control but are unvested, so that the unvested shares are one hundred
(100) percent vested."

     3.  Conflicting Terms & Survival of Agreement. Except as specifically set
         -----------------------------------------
forth herein, the Agreement shall remain in full force and effect. In the event
the terms of this Amendment shall conflict with the terms of the Agreement, the
terms of this Amendment shall control.

     4.  Counterparts. This Amendment may be executed in any number of
         ------------
counterparts, each of which shall be deemed to be an original, and all of which
together constitute one documents.

     5.  Final Agreement. The Agreement, as amended by this Amendment,
         ---------------
constitute the final agreement between the parties hereto and supercedes any
prior or contemporaneous agreement or representation, oral or written, among
them with respect to the matters set forth in the Agreement and this Amendment.

                    [Remainder of page intentionally blank]
<PAGE>

          IN WITNESS WHEREOF, the parties have executed this Amendment on the
date set forth above.

                                   COMPANY

                                   AMERIPATH, INC.

                                   By:  ____________________________________
                                        James C. New
                                        Chairman and Chief Executive Officer

                                   EXECUTIVE

                                   _____________________________________
                                   James Billington

                                       2<PAGE>

                                                                   Exhibit 10.12

                       AMENDMENT TO EMPLOYMENT AGREEMENT
                       ---------------------------------

          THIS AMENDMENT TO EMPLOYMENT AGREEMENT ("Amendment") is made this 1st
day of April, 2001, by and between AMERIPATH, INC., a Delaware corporation (the
"Company") and BRIAN C. CARR (the "Executive").

                              W I T N E S S E T H

          WHEREAS, the Company and the Executive entered into an Employment
Agreement on November 30, 2000 (the "Agreement"); and

          WHEREAS, the Company and the Executive wish to amend the Agreement.

          NOW, THEREFORE, in consideration of the Executive's continued
employment with the Company and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, the Company and the
Executive agree as follows.

          1.  Recitals.  The foregoing recitals are true and correct and are
              --------
incorporated herein by this reference.

          2.  Repayment of Relocation Expense. Delete the fourth and fifth
              -------------------------------
sentences of Subsection 4.6 and insert the following at the end of third
sentence of Subsection 4.6 of the Agreement: "The Executive shall have no
further obligation to refund any relocation expenses reimbursed by the Company."

          3.  Vesting of Options Upon and After Change in Control.  Insert the
              ---------------------------------------------------
following at the end of the first sentence in Subsection 5.6 a. of the
Agreement: "and accelerate the vesting of all AmeriPath Stock Options which have
been granted to the Executive, so that the unvested shares are one hundred (100)
percent vested."  Insert the following at the end of the second sentence in
Subsection 5.6 a. of the Agreement: "and (5) accelerate the vesting of all
AmeriPath Stock Options which have been granted to the Executive since the
Change in Control but are unvested, so that the unvested shares are one hundred
(100) percent vested."

          4.  Change in Control Anniversary Bonus.  Insert the following as
              -----------------------------------
Subsection 5.6 c. in the Agreement:

If, on the date of the one-year anniversary of the date of the Change In
Control, the Executive is in the employ of the Company, or any successor thereto
or assign thereof, the Executive shall be paid, on such one-year anniversary
date, an additional lump sum bonus equal to one times the Executive's annual
Base Salary as determined immediately prior to the Change in Control Date (the
"Anniversary Bonus").

          5.  Conflicting Terms & Survival of Agreement.  Except as specifically
              -----------------------------------------
set forth herein, the Agreement shall remain in full force and effect.  In the
event the terms of this Amendment shall conflict with the terms of the
Agreement, the terms of this Amendment shall control.
<PAGE>

          6.  Counterparts.  This Amendment may be executed in any number of
              ------------
counterparts, each of which shall be deemed to be an original, and all of which
together constitute one documents.

          7.  Final Agreement.  The Agreement, as amended by this Amendment,
              ---------------
constitute the final agreement between the parties hereto and supercedes any
prior or contemporaneous agreement or representation, oral or written, among
them with respect to the matters set forth in the Agreement and this Amendment.

          IN WITNESS WHEREOF, the parties have executed this Amendment on the
date set forth above.

                                   COMPANY

                                   AMERIPATH, INC.

                                   By:  _______________________________________
                                        James C. New
                                        Chairman and Chief Executive Officer

                                   EXECUTIVE

                                   _____________________________________
                                   Brian C. Carr

                                      2<PAGE>

                                                                    EXHIBIT 10.1

                                                                    May 29, 2001
Mr. Marvin Tancer

Dear Marvin:

     This letter shall serve to confirm the terms of employment offered to you
by Ribozyme Pharmaceuticals, Inc. (the "Company") and acknowledge your
acceptance of the employment on such terms as detailed below. Capitalized terms
used herein and not otherwise defined herein shall have the meanings ascribed to
them on Appendix 1 hereto.

     1.  Positions and Scope of Employment. As of the Commencement Date, you
         ---------------------------------
shall serve as Chief Financial Officer and Vice President of Operations of the
Company.  You shall render such business and professional services in the
performance of your duties, consistent with your position within the Company,
consistent with the Bylaws of the Company and (i) from the Commencement Date
until June 30, 2001, as shall be reasonably assigned to you by the Chief
Operating Officer of the Company, and during such period you shall report
directly to the Chief Operating Officer, and (ii) from and after July 1, 2001,
as shall reasonably be assigned to you by the Chief Executive Officer of the
Company, and you shall then report directly to the Chief Executive Officer.  You
shall perform your duties faithfully and to the best of your ability and shall
devote your full business efforts and time to the Company.  For purposes hereof
the "Commencement Date" shall be such date as you shall determine, in your sole
discretion, to commence your employment, provided however, that in no event
shall such date be later than July 1, 2001.

     2.  Compensation.
         ------------

         (a)  Base Salary. During the period beginning on the Commencement Date,
              -----------
the Company shall pay to you as compensation for your services a base salary at
the annualized rate of $250,000. Effective January 1, 2002, you shall receive a
non-prorated Base Salary increase of at least four percent (4%). After December
31, 2002 you shall be eligible for annual Base Salary increases as determined by
the Compensation Committee. Your Base Salary shall be paid in accordance with
the Company's normal payroll practices.

         (b)  Bonus.  In each year of your employment with the Company you shall
              -----
be eligible to earn a bonus. The annual bonus shall be based upon attainment of
reasonable and achievable goals which shall be mutually agreed upon by you and
the Chief Operating Officer with respect to such goals applicable to the period
from the Commencement Date through June 30, 2001, and by you and the Chief
Executive Officer with respect to such goals applicable to any period after July
1, 2001. For the period from the Commencement Date through December 31, 2001,
the amount of the annual bonus which you shall be eligible to earn shall be
equal to twenty-five percent (25%)
<PAGE>

of your annual Base Salary in effect as of the Commencement Date, and for the
period from January 1, 2002 through December 31, 2002, and for each calendar
year thereafter, the amount of the annual bonus which you shall be eligible to
earn shall be equal to twenty-five percent (25%) or more of your then annual
Base Salary as determined by the Compensation Committee. Such bonus shall be
payable in a cash lump sum within thirty (30) days after the end of the calendar
year with respect to which the bonus is payable.

          (c)  Options.  Upon the Commencement Date, the Company shall grant to
               -------
you stock options to purchase 175,000 shares of the Company's common stock which
shall be exercisable for a period of ten (10) years at an exercise price equal
to Fair Market Value (as defined in the Company's stock option plan) of the date
of the stock option grant. In subsequent years, the Company may grant to you
stock options to purchase additional shares of the Company's common stock,
exercisable for such period of time and at such exercise price as the
Compensation Committee may determine. Fifty percent (50%) of each stock option
grant shall vest, annually, in arrears, over a period of four years at the rate
of twenty-five percent (25%) per year (the "Time-Vested Options"), and the
remaining fifty percent (50%) vesting upon the attainment of reasonable and
achievable goals that shall be mutually agreed upon by you and the Chief
Executive Officer (the "Performance-Vested Options"). Each stock option grant
shall be in the form of incentive stock options in the maximum amount permitted
by applicable law.

          (d)  Employee Benefits.  During your employment with the Company, you
               -----------------
shall be entitled to participate in the employee benefit plans currently and
hereafter maintained by the Company which shall include, without limitation, the
following:

               (i)    group PPO medical and dental insurance plans (the coverage
     under which shall include your dependents and contain no restrictions
     relative to pre-existing conditions and no waiting period prior to coverage
     becoming effective);

               (ii)   short-term disability insurance and long-term disability
     insurance (which coverage shall contain no restrictions relative to pre-
     existing conditions);

               (iii)  term life insurance in the amount of $250,000, with your
     having the right to designate the beneficiary(ies) thereof;

               (iv)   participation (eligible on the first plan entry date
     following the six-month anniversary of the Commencement Date) in the
     Company's 401(k) plan, your contributions to which may be matched by the
     Company with contributions of shares of its common stock if approved by the
     Board; provided that any such matching contributions shall vest over three
     (3) years of service;

               (v)    participation in the Company's Flexible Spending Account;
     and

               (vi)   participation (within six (6) months after the
     Commencement Date) in the Company's Stock Purchase Plan, allowing purchase
     of shares of the Company's common stock at fifteen percent (15%) below the
     market price.

                                      -2-
<PAGE>

          The Company reserves the right to revise, add or rescind any benefits
at any time for its employees.

          (e)  Vacation Days; Sick Days; Holidays.  You shall be entitled to
               -----------------------------------
paid vacation, sick days and holidays in accordance with the Company's policies
as in effect from time to time.

          (f)  Expenses. The Company shall reimburse you for reasonable travel,
               --------
entertainment or other expenses incurred by you in the furtherance of or in
connection with the performance of your duties hereunder, in accordance with the
Company's expense reimbursement policy as in effect from time to time.

     3.   Loan.  On the Commencement Date, the Company shall provide to you an
          ----
interest-free loan in the amount of $200,000 (the "Loan").  Subject to the
provisions hereof, the Company shall forgive twenty percent (20%) of the
original principal amount of the Loan on each anniversary of the Commencement
Date until the Loan has been fully forgiven, provided, however, that the Loan
shall be fully forgiven in the event of termination of your employment due to
your death or permanent disability (as hereinafter defined). In the event that
it shall be determined that any payment shall be due by you for taxes of any
kind or nature relating to the forgiveness of the Loan or the imputation of
interest in connection therewith ("Taxes"), the Company shall deliver to you an
additional payment in an amount such that, after payment of any taxes applicable
to such additional payment by the Company, the net amount available to you after
payment of all such taxes shall be equal to the Taxes payable by you, together
with any interest or penalties associated therewith (a "Gross-Up Payment").

     4.   Relocation Expenses.  The Company  agrees that it shall pay or
          -------------------
reimburse you for all reasonable out-of-pocket relocation and relocation-related
expenses which may be billed directly to the Company or paid by you and
submitted for reimbursement, including, without limitation, the following:

               (a)  costs of services of moving companies (including packing,
                    transportation and relocation expenses, including the
                    transportation of automobiles);
               (b)  costs associated with your search for a new residence
                    (including, without limitation, the costs of airfare,
                    automobile rental, meals and hotel accommodations for
                    yourself and your immediate family);
               (c)  commissions payable to brokers in connection with the sale
                    of your current residence;
               (d)  costs attendant to the sale of your current residence and
                    the purchase of a new residence in the Boulder, Colorado
                    area (including, without limitation, the costs of home
                    inspections, survey, appraisal, title insurance, transfer
                    fees, attorneys' fees, accountants' fees and closing costs);
               (e)  loan origination fees (points) related to the purchase of
                    your new residence in an amount of up to three percent (3%)
                    of the loan amount;
               (f)  costs associated with commuting from your current residence
                    to the Company's offices (including, without limitation, the
                    costs of airfare, automobile rental, meals and hotel
                    accommodations for you) for a

                                      -3-
<PAGE>

                    period of up to three (3) months, subject to extension upon
                    our mutual agreement;
               (g)  automobile rental charges prior to establishment of a
                    permanent residence in Boulder, Colorado;
               (h)  rent and other expenses associated with temporary housing
                    for yourself and your immediate family until the earlier of
                    (i) six (6) months following the Commencement Date or (ii)
                    the sale and closing of your current residence, subject to
                    extension upon our mutual agreement;
               (i)  the Company agrees to make available to you upon your
                    request an interest free bridge loan in the amount of up to
                    $1,400,000 for a term of up to six (6) months, subject to
                    increase and/or extension upon our mutual agreement. The
                    Company will receive a secured interest in the property
                    secondary to any first mortgage; and
               (j)  payment of any duplicate mortgage loan payments and house
                    expenses (related to your current residence) to preclude
                    your paying for your current residence and your new
                    residence concurrently for a period of up to six (6) months
                    after the purchase and closing of title on your new
                    residence, subject to extension upon our mutual agreement.

     All such payments shall be subject to the Company receiving reasonably
acceptable documentation evidencing the incurring of such cost, expense or fee.
In the event that it shall be determined that any payment shall be due by you
for taxes of any kind or nature relating to amounts paid to you or on your
behalf by the Company in connection with your relocation as provided above, the
Company shall deliver to you a Gross-Up Payment, except that no such Gross-Up
Payment shall be payable by the Company with respect to the interest free bridge
loan described in clause (i) above.

     5.   Termination.
          ------------

          (a)  At-Will Employment.  You and the Company agree that your
               ------------------
employment with the Company shall be "at-will" employment, that you are free to
resign and, subject to the provisions hereof, the Company is free to terminate
your employment at any time, without notice, procedure or formality, with or
without Cause (for any reason or no reason).

          (b)  Voluntary Termination; Termination for Cause.  In the event that
               --------------------------------------------
your employment with the Company is terminated voluntarily by you or for Cause
by the Company, then (i) all options which have vested shall continue to be
exercisable in accordance with the terms of the Company's stock option plan and
applicable legal requirements; (ii) all payments of Base Salary and bonuses
accrued but unpaid on the date of termination, as well as all expenses incurred
to the date of termination, shall be due and payable to you immediately and all
further compensation by the Company to you hereunder shall terminate as of the
date of termination; (iii) the unforgiven balance of the Loan shall be repaid by
you within thirty (30) days of the date of termination; and (iv) you shall be
entitled to continue medical and dental insurance coverage for yourself and your
dependents, at your expense, at the same level of coverage as was provided to
the you under the Company's insurance plan immediately prior to the termination
("Health Care Coverage") by electing COBRA continuation coverage ("COBRA") in
accordance with applicable law.

                                      -4-
<PAGE>

          (c)  Termination upon Death or Disability.  In the event that your
               ------------------------------------
employment with the Company is terminated as a result of your death or permanent
disability then (i) all options which have vested shall continue to be
exercisable in accordance with the terms of the Company's stock option plan and
applicable legal requirements; (ii) the Company shall pay to you or your estate,
as applicable, all payments of Base Salary and bonuses accrued but unpaid on the
date of termination, as well as expenses incurred to the date of termination,
immediately upon the date of termination and all further compensation by the
Company to you hereunder shall terminate as of the date of termination, (iii)
the Company shall forgive all amounts owed by you or your estate, as applicable,
in connection with the Loan and make any necessary Gross-Up Payment; (iv) you
shall be entitled to continue medical and dental insurance coverage for yourself
and your dependents, at your expense, at the same level of coverage as was
provided to you under the Company's Health Care Coverage by electing COBRA in
accordance with applicable law. For purposes hereof, the term "permanent
disability" shall mean your inability to perform your duties hereunder on
account of illness, accident or other physical or mental incapacity which shall
continue for a consecutive period of ninety (90) days or an aggregate of one
hundred twenty (120) days in any consecutive twelve-month period.

          (d)  Termination without Cause or for Good Reason.  In the event that
               --------------------------------------------
your employment with the Company is terminated by the Company without Cause or
by you for Good Reason, then (i) all options which have vested shall continue to
be exercisable in accordance with the terms of the Company's stock option plan
and applicable legal requirements; (ii) all payments of Base Salary and bonuses
accrued but unpaid on the date of termination, as well as all expenses incurred
to the date of termination, shall be due and payable to you immediately; (iii)
subject to the provisions of Section 6 hereof, all unvested options shall vest
immediately prior to such termination of employment to the extent that such
options would have vested from the last annual vesting anniversary date (or, if
none has yet occurred because such termination of your employment occurs prior
to the first such anniversary date, the date of grant of such stock options)
through the date of termination of your employment on a monthly basis, in equal
installments, at the rate of one forty-eighth (1/48) of such stock option grant
per month; (iv) the Company shall forgive all amounts owed by you in connection
with the Loan and make any necessary Gross-Up Payment; (v) the Company shall pay
to you a severance payment, in a cash lump sum, equal to 9 months of your Base
Salary plus 9 months of your annual target bonus (the annual target bonus shall
be based upon the average percentage of historical achievement applicable to the
2001 and later calendar years or, if such termination of employment shall occur
during the 2001 calendar year, one hundred percent (100%) of the full target
bonus for the 2001 calendar year) provided, however, that in the event that the
termination is a result of a Change of Control (whether due to termination
without Cause or your termination for Good Reason following a Change of Control)
the amount of such severance payment shall be no less than 12 months' severance;
and (vi) the Company shall be responsible for all costs relating to maintaining
your Health Care Coverage for you and your dependents under COBRA for the longer
of the amount of months to which the severance payment applies as set forth in
subsection (d) or for so long as allowed by law.

     6.   Change of Control.  Notwithstanding anything to the contrary contained
          -----------------
herein, in the event of a Change of Control of the Company, then (i) all options
which have vested shall continue to be exercisable in accordance with the
Company's stock option plan and applicable legal requirements; (ii) fifty
percent (50%) of the unvested Time-Vested Options shall vest immediately prior
to the Change of Control (it being understood and agreed that the Board may
increase at any

                                      -5-
<PAGE>

time such percentage vesting upon the occurrence of a Change of Control); (iii)
the Company shall forgive all amounts owed by you in connection with the Loan
and make any necessary Gross-Up Payment; (iv) to the extent that such Change of
Control results in your termination, whether by the Company without Cause or by
you for Good Reason, the Company shall pay to you a severance payment in
accordance with the provisions of Section 5(d) above. Notwithstanding the
foregoing, to the extent that the acceleration of vesting as contemplated in
clause (ii) above shall cause the options to not qualify as incentive stock
options under applicable tax laws, you shall be entitled to require that the
Company not accelerate the vesting of all or part of your unvested stock options
in such manner as shall preserve the status of the options as incentive stock
options.

     7.   Non-Disclosure/Invention Assignment Agreement.  You agree to enter
          ---------------------------------------------
into the Company's standard Non-Disclosure and Invention Assignment Agreement
upon commencing employment hereunder, in the forms of Attachment A and
                                                      ------------
Attachment B hereto.
------------

     8.   Directors' and Officers' Liability Policy.  You will be covered under
          -----------------------------------------
the Company's directors' and officers' liability insurance policy, which shall
provide coverage in an amount and upon terms customary to similarly situated
companies. The Company shall maintain such policy throughout the duration of
your employment.

     9.   Expenses associated with this Agreement.  The Company shall reimburse
          ---------------------------------------
you for all expenses incurred by you in the preparation, review and negotiation
of this Agreement, including, without limitation, reasonable attorneys' fees and
accountants' fees.

     10.  Indemnification.  The Company agrees that if you are made a party or
          ---------------
are threatened to be made a party to any action, suit or proceeding, whether
civil, criminal, administrative or investigative (a "Proceeding"), by reason of
the fact that you are or were a director or officer of the Company or any
subsidiary or affiliate of the Company, whether or not the basis of such
Proceeding is alleged action in an official capacity as a director, officer,
employee or agent, you shall be indemnified and held harmless by the Company to
the fullest extent authorized by Delaware law, as the same exists or may
hereafter amended, against all damages, losses, judgments, liabilities, fines,
penalties, excise taxes, settlements and costs, including reasonable attorneys'
fees, accountants' fees and disbursement, incurred or suffered by you in
connection therewith (including the advancement of your defense costs and
expenses as and when incurred) and such indemnification shall continue as to you
even if you have ceased to be an officer, director or agent and are no longer
employed by the Company and shall inure to the benefit of your heirs, executors
and administrators.

     11.  Assignment.  This Agreement shall be binding upon and inure to the
          ----------
benefit of (a) your heirs, executors and legal representatives upon your death
and (b) any successor of the Company. Any such successor of the Company shall be
deemed substituted for the Company under the terms of this Agreement for all
purposes. For this purpose, "successor" means any person, firm, corporation or
other business entity which at any time, whether by purchase, merger or
otherwise, directly or indirectly acquires all or substantially all of the
assets or business of the Company.

     12.  Notices.  All notices, requests, demands and other communications
          -------
provided hereunder shall be in writing and shall be deemed given (i) on the date
of delivery if delivered personally, (ii) one (1) day after being sent by a well
established commercial overnight service, or (iii) four (4) days after being
mailed by registered or certified mail, return receipt requested, prepaid

                                      -6-
<PAGE>

and addressed to the parties or their successors at the following addresses, or
at such other addresses as the parties may later designate in writing:

          If to the Company:

          RIBOZYME PHARMACEUTICALS, INC.
          2950 Wilderness Place
          Boulder, Colorado 80301
          Attn: Chief Executive Officer

          If to you:

          at the last residential address known by the Company.

     13.  Severability.  In the event that any provision hereof becomes or is
          ------------
declared by a court of competent jurisdiction to be illegal, unenforceable or
void, this Agreement shall continue in full force and effect without said
provision.

     14.  Integration. This Agreement, together with the Non-Disclosure and
          -----------
Invention Assignment Agreement represents the entire agreement and understanding
between the parties as to the subject matter herein and supersedes all prior or
contemporaneous agreements whether written or oral. No waiver, alteration, or
modification of any of the provisions of this Agreement shall be binding unless
in writing and signed by duly authorized representatives of the parties hereto.

     15.  Governing Law.  This Agreement shall be governed by and interpreted in
          -------------
accordance with the laws of the State of Colorado, without reference to
principles of conflict of laws.

     16.  Expiration Date.  This offer set forth in this letter agreement will
          ---------------
expire on June 10, 2001, unless you have signed this letter agreement where
indicated below and returned it to the undersigned before the close of business
on such date.

     Please sign this agreement and return one signed original copy to me,
acknowledging your agreement with and acceptance of these terms of employment.

                                         Sincerely,

                                         RIBOZYME PHARMACEUTICALS, INC.

                                         By: /s/ Ralph E. Christoffersen
                                             -----------------------------------
                                                 Ralph E. Christoffersen, Ph.D.
                                                 Chief Executive Officer

Agreed and accepted:

/s/ Marvin Tancer
-------------------------
Marvin Tancer

Dated: June 6, 2001

                                      -7-
<PAGE>

                                                                      Appendix 1

                                  DEFINITIONS

     Cause.  "Cause" is defined as (i) conviction of a felony crime involving
     -----
moral turpitude, (ii) an intentional action or intentional failure to act which
was performed in bad faith and to the material detriment of the Company, (iii)
continued intentional refusal or intentional failure to act in accordance with
any lawful and proper direction or order of the Board, (iv) willful and habitual
neglect of the duties of employment, (v) breach of the Non-Disclosure Agreement,
contemplated hereunder, or (vi) breach of this agreement; provided, however,
that with respect to the events of "cause" described under clauses (iv) and (vi)
above, the Company shall have first provided to you written notice describing
the nature of the event and, thereafter, provided a reasonable opportunity to
cure such event, which reasonable opportunity shall in no event be less than
thirty (30) days following receipt of such notice.

     Change of Control. "Change of Control" of the Company is defined as: (i)
     -----------------
any "person" (as such term is used in Sections 13(d) and 14(d) of the Securities
Exchange Act of 1934, as amended) becomes the "beneficial owner" (as defined in
Rule 13d-3 under said Act), directly or indirectly, of securities of the Company
representing fifty percent (50%) or more of the total voting power represented
by the Company's then outstanding voting securities; or (ii) the consummation of
a merger or consolidation of the Company with any other corporation that has
been approved by the stockholders of the Company, other than a merger or
consolidation which would result in the voting securities of the Company
outstanding immediately prior thereto continuing to represent (either by
remaining outstanding or by being converted into voting securities of the
surviving entity) more than fifty percent (50%) of the total voting power
represented by the voting securities of the Company or such surviving entity
outstanding immediately after such merger or consolidation, or the stockholders
of the Company approve a plan of complete liquidation of the Company; or (iii)
the consummation of  the sale or disposition by the Company of all or
substantially all the Company's assets; or (iv) when the individuals who on the
date hereof constitute the Board and any new director (other than a director
designated by a person or entity who has entered into an agreement to effect a
transaction described in clause (ii) or (iii) above), whose nomination and/or
election to the Board was approved by a vote of at least a majority of the
directors still in office who either were directors on the date hereof or whose
election or nomination for election was previously approved, cease for any
reason to constitute a majority of the Board.

     Good Reason. "Good Reason" is defined as your voluntary resignation from
     -----------
your employment with the Company upon the occurrence of any of the following
without your express written consent: (i) the assignment to you of any duties or
responsibilities inconsistent with the scope of the duties or responsibilities
associated with your titles or positions or any diminution to or adverse change
of your titles, positions, status or circumstances of employment; (ii) a
reduction by the Company in your Base Salary or bonus target percentage or,
absent a good business reason, of  the facilities, benefits and perquisites
available to you immediately prior to such reduction; (iii) the taking of any
action by the Company which would adversely affect your participation in, or
reduce your benefits under, the Company's benefit plans (including equity
benefits) as of the date of

                                      -8-
<PAGE>

execution hereof, except to the extent that the benefits of all other employees
of the Company are similarly reduced; provided, that regardless of whether the
Company may similarly reduce the benefits of other employees, it shall
constitute Good Reason in the event the Company takes any action which would
adversely affect your participation in, or adversely affect or reduce in any
material aspect your benefits under, the Company's medical, dental, short-term
disability and/or long-term disability benefit plans or arrangements; (iv) a
relocation of your principal office to a location more than thirty (30) miles
from Boulder, Colorado, except for reasonable periods of required travel on
Company business; (v) any breach by the Company of any material provision of
this Agreement; (vi) the occurrence of a Change of Control, provided that your
resignation occurs within the first six (6) months following the Change of
Control; or (vii) any failure by the Company to obtain the assumption of this
Agreement in writing by any successor or assign of the Company; provided,
however, that with respect to the events of "Good Reason" described in clauses
(i) through (vii) above, you shall have first provided to the Company written
notice describing the nature of the event and, thereafter, provided the Company
with a reasonable opportunity to cure such event, which reasonable opportunity
shall in no event be less than thirty (30) days following receipt of such
notice.

                                      -9-

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