Document:

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                                                                     Exhibit 4.5

                         REGISTRATION RIGHTS AGREEMENT
                         -----------------------------

          This Registration Rights Agreement is made and entered into as of
October 27, 2000 (this "Agreement"), by and between Myriad Genetics Inc., a
Delaware corporation (the "Company"), and Acqua Wellington North American
Equities Fund, Ltd., a limited liability company organized under the laws of the
Commonwealth of the Bahamas (the "Purchaser")

          This Agreement is being entered into pursuant to the Purchase
Agreement, dated as of the date hereof, by and between the Company and the
Purchaser (the "Purchase Agreement").
                ------------------

          The Company and the Purchaser hereby agree as follows:

     1.   Definitions.
          -----------

          Capitalized terms used and not otherwise defined herein shall have the
meanings given such terms in the Purchase Agreement.  As used in this Agreement,
the following terms shall have the following meanings:

          Capitalized terms used and not otherwise defined herein shall have the
meanings given such terms in the Purchase Agreement.  As used in this Agreement,
the following terms shall have the following meanings:

          "Advice" shall have the meaning set forth in Section 3(m).
           ------

          "Affiliate" means, with respect to any Person, any other Person that
           ---------
directly or indirectly controls or is controlled by or under common control with
such Person.  For the purposes of this definition, "control," when used with
                                                    -------
respect to any Person, means the possession, direct or indirect, of the power to
direct or cause the direction of the management and policies of such Person,
whether through the ownership of voting securities, by contract or otherwise;
and the terms of "affiliated," "controlling" and "controlled" have meanings
                  ----------    -----------       ----------
correlative to the foregoing.

          "Blackout Period" shall have the meaning set forth in Section 3(n).
           ---------------

          "Board" shall have the meaning set forth in Section 3(n).
           -----

          "Business Day" means any day except Saturday, Sunday and any day which
           ------------
shall be a legal holiday or a day on which banking institutions in the state of
New York generally are authorized or required by law or other government actions
to close.

          "Commission" means the Securities and Exchange Commission.
           ----------

          "Common Stock" means the Company's Common Stock, par value $0.01 per
           ------------
share.
<PAGE>

          "Effectiveness Date" means with respect to the Registration Statement
           ------------------
the earlier of the 90th day following the Closing Date, before which the Company
will use its best efforts to cause the registration statement to become
effective, and the date which is within five (5) Business Days of the date on
which the Commission informs the Company that the Commission (i) will not review
the Registration Statement or (ii) that the Company may request the acceleration
of the effectiveness of the Registration Statement.

          "Effectiveness Period" shall have the meaning set forth in Section 2.
           --------------------

          "Event" shall have the meaning set forth in Section 7(e).
           -----

          "Exchange Act" means the Securities Exchange Act of 1934, as amended.
           ------------

          "Filing Date" means the date the Registration Statement is filed which
           -----------
date shall be no later than the 30th day following the Closing Date.

          "Holder" or "Holders" means the holder or holders, as the case may be,
           ------      -------
from time to time of Registrable Securities including, including without
limitation, the Purchaser and its assignees.

          "Indemnified Party" shall have the meaning set forth in Section 5(c).
           -----------------

          "Indemnifying Party" shall have the meaning set forth in Section 5(c).
           ------------------

          "Liquidated Damages" shall have the meaning set forth in Section 7(e).
           ------------------

          "Losses" shall have the meaning set forth in Section 5(a).
           ------

          "Nasdaq" shall mean the Nasdaq National Market.
           ------

          "Person" means an individual or a corporation, partnership, trust,
           ------
incorporated or unincorporated association, joint venture, limited liability
company, joint stock company, government (or an agency or political subdivision
thereof) or other entity of any kind.

          "Proceeding" means an action, claim, suit, investigation or proceeding
           ----------
(including, without limitation, an investigation or partial proceeding, such as
a deposition), whether commenced or threatened.

          "Prospectus" means the prospectus included in the Registration
           ----------
Statement (including, without limitation, a prospectus that includes any
information previously omitted from a prospectus filed as part of an effective
registration statement in reliance upon Rule 430A promulgated under the
Securities Act), as amended or supplemented by any prospectus supplement, with
respect to the terms of the offering of any portion of the Registrable
Securities covered by the Registration Statement, and all other amendments and
supplements to the Prospectus, including post-effective amendments, and all
material incorporated by reference in such Prospectus.

                                      -2-

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          "Registrable Securities" means (i) the shares of Common Stock issued
           ----------------------
pursuant to the Purchase Agreement (the "Common Shares") and upon any stock
split, stock dividend, recapitalization or similar event with respect to such
Common Shares, and (ii) any other dividend or other distribution with respect
to, conversion or exchange of, or in replacement of, Registrable Securities.

          "Registration Statement" means the registration statement and any
           ----------------------
additional registration statements contemplated by Section 2, including (in each
case) the Prospectus, amendments and supplements to such registration statement
or Prospectus, including pre- and post-effective amendments, all exhibits
thereto, and all material incorporated by reference in such registration
statement.

          "Rule 144" means Rule 144 promulgated by the Commission pursuant to
           --------
the Securities Act, as such Rule may be amended from time to time, or any
similar rule or regulation hereafter adopted by the Commission having
substantially the same effect as such Rule.

          "Rule 158" means Rule 158 promulgated by the Commission pursuant to
           --------
the Securities Act, as such Rule may be amended from time to time, or any
similar rule or regulation hereafter adopted by the Commission having
substantially the same effect as such Rule.

          "Rule 415" means Rule 415 promulgated by the Commission pursuant to
           --------
the Securities Act, as such Rule may be amended from time to time, or any
similar rule or regulation hereafter adopted by the Commission having
substantially the same effect as such Rule.

          "Securities Act" means the Securities Act of 1933, as amended.
           --------------

          "Special Counsel" means any special counsel to the Holders, for which
           ---------------
the Holders will be reimbursed by the Company pursuant to Section 4.

     2.   Registration.  On or prior to the Filing Date, the Company shall
          ------------
prepare and file with the Commission a "shelf" Registration Statement covering
all Registrable Securities for an offering to be made on a continuous basis
pursuant to Rule 415. The Registration Statement shall be on Form S-3 (except if
the Company is not then eligible to register for resale the Registrable
Securities on Form S-3, in which case such registration shall be on another
appropriate form in accordance herewith). The Company shall use its best efforts
to cause the Registration Statement to be declared effective under the
Securities Act (including filing with the Commission a request for acceleration
of effectiveness in accordance with Rule 12dl-2 promulgated under the Exchange
Act within five (5) Business Days of the date that the Company is notified
(orally or in writing, whichever is earlier) by the Commission that a
Registration Statement will not be "reviewed," or not be subject to further
review) as soon as possible after the filing thereof, but in any event prior to
the Effectiveness Date, and to keep such Registration Statement continuously
effective under the Securities Act until such date as is the earlier of (x) the
date when all Registrable Securities covered by such Registration Statement have
been sold or (y) the date on which the Registrable Securities may be sold
without any restriction pursuant to Rule 144(k) as determined by the counsel to
the Company pursuant to a written opinion letter, addressed to the Company's
transfer agent to such effect (the "Effectiveness Period").
                                    --------------------

                                      -3-

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     3.   Registration Procedures.
          -----------------------

          In connection with the Company's registration obligations hereunder,
the Company shall:

          (a)  Prepare and file with the Commission on or prior to the Filing
Date, a Registration Statement on Form S-3 (or if the Company is not then
eligible to register for resale the Registrable Securities on Form S-3 such
registration shall be on another appropriate form in accordance herewith) in
accordance with the method or methods of distribution thereof as specified by
the Holders (except if otherwise directed by the Holders), and use its best
efforts to cause the Registration Statement to become effective and remain
effective as provided herein; provided, however, that not less than three (3)
                              --------  -------
Business Days prior to the filing of the Registration Statement or any related
Prospectus or any amendment or supplement thereto (including any document that
would be incorporated therein by reference), the Company shall (i) furnish to
the Holders and any Special Counsel, copies of all such documents proposed to be
filed, which documents (other than those incorporated by reference) will be
subject to the review of such Holders and such Special Counsel, and (ii) at the
request of any Holder cause its officers and directors, counsel and independent
certified public accountants to respond to such inquiries as shall be necessary,
in the reasonable opinion of counsel to such Holders, to conduct a reasonable
investigation within the meaning of the Securities Act. The Company shall not
file the Registration Statement or any such Prospectus or any amendments or
supplements thereto containing information about the Holders or the distribution
of securities owned by the Holders ("Holder Information") if the Holders of a
majority of the Registrable Securities or any Special Counsel shall reasonably
object in writing within three (3) Business Days of their receipt thereof to any
of the Holder Information unless the Company has received an opinion of counsel
to the effect that such disclosure is required by applicable law, rules or
regulations (including Nasdaq regulations).

          (b)  Prepare and file with the Commission such amendments, including
post-effective amendments, to the Registration Statement as may be necessary to
keep the Registration Statement continuously effective as to the applicable
Registrable Securities for the Effectiveness Period and prepare and file with
the Commission such additional Registration Statements in order to register for
resale under the Securities Act all of the Registrable Securities; (ii) cause
the related Prospectus to be amended or supplemented by any required Prospectus
supplement, and as so supplemented or amended to be filed pursuant to Rule 424
(or any similar provisions then in force) promulgated under the Securities Act;
(iii) respond as promptly as practicable to any comments received from the
Commission with respect to the Registration Statement or any amendment thereto
and as promptly as practicable provide the Holders true and complete copies of
all correspondence from and to the Commission relating to the Registration
Statement; and (iv) comply in all material respects with the provisions of the
Securities Act and the Exchange Act with respect to the disposition of all
Registrable Securities covered by the Registration Statement during the
applicable period in accordance with the intended methods of disposition by the
Holders thereof set forth in the Registration Statement as so amended or in such
Prospectus as so supplemented.

                                      -4-
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          (c)  Notify the Holders of Registrable Securities to be sold and any
Special Counsel as promptly as practicable (and, in the case of (i)(A) below,
not less than three (3) Business Days prior to such filing) and (if requested by
any such Person) confirm such notice in writing no later than one (1) Business
Day following the day (i)(A) when a Prospectus or any Prospectus supplement or
post-effective amendment to the Registration Statement is proposed to be filed;
(B) when the Commission notifies the Company whether there will be a "review" of
such Registration Statement and whenever the Commission comments in writing on
such Registration Statement and (C) with respect to the Registration Statement
or any post-effective amendment, when the same has become effective; (ii) of any
request by the Commission or any other Federal or state governmental authority
for amendments or supplements to the Registration Statement or Prospectus or for
additional information with respect to the Registration Statement or the
Prospectus; (iii) of the issuance by the Commission of any stop order suspending
the effectiveness of the Registration Statement covering any or all of the
Registrable Securities or the initiation of any Proceedings for that purpose;
(iv) of the receipt by the Company of any notification with respect to the
suspension of the qualification or exemption from qualification of any of the
Registrable Securities for sale in any jurisdiction, or the initiation or
threatening of any Proceeding for such purpose; and (v) of the occurrence of any
event that makes any statement made in the Registration Statement or Prospectus
or any document incorporated or deemed to be incorporated therein by reference
untrue in any material respect or that requires any revisions to the
Registration Statement, Prospectus or other documents so that, in the case of
the Registration Statement or the Prospectus, as the case may be, it will not
contain any untrue statement of a material fact or omit to state any material
fact required to be stated therein or necessary to make the statements therein,
in the light of the circumstances under which they were made, not misleading.

          The Company shall promptly furnish to Special Counsel, without charge,
(i) any correspondence from the Commission or the Commission's staff to the
Company or its representatives relating to any Registration Statement and (ii)
promptly after the same is prepared and filed with the Commission, a copy of any
written response to the correspondence received from the Commission.

          (d)  Use its best efforts to avoid the issuance of, or, if issued,
obtain the withdrawal of, (i) any order suspending the effectiveness of the
Registration Statement or (ii) any suspension of the qualification (or exemption
from qualification) of any of the Registrable Securities for sale in any
jurisdiction, at the earliest practicable moment.

          (e)  If requested by the Holders of a majority in interest of the
Registrable Securities, (i) promptly incorporate in a Prospectus supplement or
post-effective amendment to the Registration Statement such information as the
Company reasonably agrees should be included therein and (ii) make all required
filings of such Prospectus supplement or such post-effective amendment as soon
as practicable after the Company has received notification of the matters to be
incorporated in such Prospectus supplement or post-effective amendment.

          (f)  Furnish to each Holder and any Special Counsel, without charge,
at least one conformed copy of each Registration Statement and each amendment
thereto, including financial statements and schedules, all documents
incorporated or deemed to be incorporated therein by reference, and all exhibits
to the extent requested by such Person (including those

                                      -5-
<PAGE>

previously furnished or incorporated by reference) as soon as practicable after
the filing of such documents with the Commission.

          (g)  Promptly deliver to each Holder and any Special Counsel, without
charge, as many copies of the Registration Statement, Prospectus or Prospectuses
(including each form of prospectus) and each amendment or supplement thereto as
such Persons may reasonably request; and the Company hereby consents to the
lawful use of such Prospectus and each amendment or supplement thereto by each
of the selling Holders in connection with the offering and sale of the
Registrable Securities covered by such Prospectus and any amendment or
supplement thereto.

          (h)  Prior to any public offering of Registrable Securities, use its
best efforts to register or qualify or cooperate with the selling Holders and
any Special Counsel in connection with the registration or qualification (or
exemption from such registration or qualification) of such Registrable
Securities for offer and sale under the securities or Blue Sky laws of such
jurisdictions within the United States as any Holder requests in writing, to
keep each such registration or qualification (or exemption therefrom) effective
during the Effectiveness Period and use its commercially reasonable best efforts
to do any and all other acts or things reasonably necessary or advisable to
enable the disposition in such jurisdictions of the Registrable Securities
covered by a Registration Statement; provided, however, that the Company shall
                                     --------  -------
not be required to qualify generally to do business in any jurisdiction where it
is not then so qualified or to take any action that would subject it to general
service of process in any such jurisdiction where it is not then so subject or
subject the Company to any tax in any such jurisdiction where it is not then so
subject.

          (i)  Cooperate with the Holders to facilitate the timely preparation
and delivery of certificates representing Registrable Securities to be sold
pursuant to a Registration Statement, which certificates shall be free of all
restrictive legends, and to enable such Registrable Securities to be in such
denominations and registered in such names as any Holder may request at least
two (2) Business Days prior to any sale of Registrable Securities.

          (j)  Upon the occurrence of any event contemplated by Section 3(c)(v),
as promptly as practicable, prepare a supplement or amendment, including a post-
effective amendment, to the Registration Statement or a supplement to the
related Prospectus or any document incorporated or deemed to be incorporated
therein by reference, and file any other required document so that, as
thereafter delivered, neither the Registration Statement nor such Prospectus
will contain an untrue statement of a material fact or omit to state a material
fact required to be stated therein or necessary to make the statements therein,
in the light of the circumstances under which they were made, not misleading.

          (k)  Use its best efforts to cause all Registrable Securities relating
to such Registration Statement to be listed on Nasdaq and any other securities
exchange, quotation system, market or over-the-counter bulletin board, if any,
on which the same securities issued by the Company are then listed as and when
required pursuant to the Purchase Agreement, and will comply in all material
respects with the Company's reporting, filing and other obligations under the
bylaws or rules of the National Association of Securities Dealers, Inc. and the
Nasdaq system or any other applicable market or system.

                                      -6-
<PAGE>

          (l)  Comply in all material respects with all applicable rules and
regulations of the Commission and make generally available to its security
holders earning statements satisfying the provisions of Section 11(a) of the
Securities Act and Rule 158 not later than forty-five (45) days after the end of
any twelve (12)-month period (or ninety (90) days after the end of any twelve
(12)-month period if such period is a fiscal year) commencing on the first day
of the first fiscal quarter of the Company after the effective date of the
Registration Statement, which statement shall conform to the requirements of
Rule 158.

          The Purchaser and each selling Holder whose shares are covered by a
Registration Statement shall furnish to the Company information regarding such
Holder and the distribution of such Registrable Securities as is required by law
to be disclosed in the Registration Statement, and the Company may exclude from
such registration the Registrable Securities of any such Holder who fails to
furnish such information within a reasonable time prior to the filing of each
Registration Statement, supplemented Prospectus and/or amended Registration
Statement. If any Registration Statement or Prospectus refers to any Holder by
name or otherwise as the Holder of any securities of the Company, then such
Holder shall promptly notify the Company of any fact of which the Holder becomes
aware and the happening of any event which relates to the Holder or distribution
of such securities owned by such Holder which results in the Registration
Statement or the Prospectus included in such Registration Statement containing
an untrue statement of material fact or omitting to state a material fact
required to be stated therein or necessary to make the statements therein not
misleading and shall provide to the Company such information as shall be
necessary to enable the Company to prepare a supplement or post-effective
Amendment to such Registration Statement or Prospectus or any document
incorporated therein by reference or file any other document required so that
the Registration Statement or Prospectus will not contain an untrue statement of
material fact or omit to state a material fact required to be stated therein.

          If the Registration Statement refers to any Holder by name or
otherwise as the holder of any securities of the Company, then such Holder shall
have the right to require (if such reference to such Holder by name or otherwise
is not required by the Securities Act or any similar federal statute then in
force) the deletion of the reference to such Holder in any amendment or
supplement to the Registration Statement filed or prepared subsequent to the
time that such reference ceases to be required.

          Each Holder covenants and agrees that (i) it will not sell any
Registrable Securities under the Registration Statement until it has received
copies of the Prospectus as then amended or supplemented as contemplated in
Section 3(g) and notice from the Company that such Registration Statement and
any post-effective amendments thereto have become effective as contemplated by
Section 3(c) and (ii) it and its officers, directors or Affiliates, if any, will
comply with the prospectus delivery requirements of the Securities Act as
applicable to them in connection with sales of Registrable Securities pursuant
to the Registration Statement.

          Each Holder agrees by its acquisition of such Registrable Securities
that, upon receipt of a notice from the Company of the occurrence of any event
of the kind described in Section 3(c)(ii), 3(c)(iii), 3(c)(iv) or 3(c)(v), such
Holder will forthwith discontinue disposition of such Registrable Securities
under the Registration Statement until such Holder's receipt of the copies of
the supplemented Prospectus and/or amended Registration Statement contemplated
by

                                      -7-
<PAGE>

Section 3(j), or until it is advised in writing (the "Advice") by the Company
                                                      ------
that the use of the applicable Prospectus may be resumed, and, in either case,
has received copies of any additional or supplemental filings that are
incorporated or deemed to be incorporated by reference in such Prospectus or
Registration Statement.

          (m)  If (i) there is material non-public information regarding the
Company which the Company's Board of Directors (the "Board") reasonably
                                                     -----
determines not to be in the Company's best interest to disclose and which the
Company is not otherwise required to disclose, or (ii) there is a significant
business opportunity (including, but not limited to, the acquisition or
disposition of assets (other than in the ordinary course of business) or any
merger, consolidation, tender offer or other similar transaction) available to
the Company which the Board reasonably determines not to be in the Company's
best interest to disclose and which the Company would be required to disclose
under the Registration Statement, then the Company may suspend effectiveness of
a registration statement and suspend the sale of Registrable Securities under a
Registration Statement for a period not to exceed thirty (30) consecutive days,
provided that the Company may not suspend its obligation under this Section 3(m)
for more than forty-five (45) days in the aggregate during any twelve (12) month
period (each, a "Blackout Period"); provided, however, that no such suspension
                 ----------------   --------  -------
shall be permitted for consecutive thirty (30) day periods, arising out of the
same set of facts, circumstances or transactions.

          (n)  Within two (2) business days after the Registration Statement
which includes the Registrable Securities is ordered effective by the
Commission, the Company shall deliver, and shall cause legal counsel for the
Company to deliver, to the transfer agent for such Registrable Securities (with
copies to the Holders whose Registrable Securities are included in such
Registration Statement) confirmation that the Registration Statement has been
declared effective by the Commission in the form attached hereto as Exhibit A.
                                                                    ---------

     4.   Registration Expenses.
          ---------------------

          All fees and expenses incident to the performance of or compliance
with this Agreement by the Company shall be borne by the Company whether or not
the Registration Statement is filed or becomes effective and whether or not any
Registrable Securities are sold pursuant to the Registration Statement.  The
fees and expenses referred to in the foregoing sentence shall include, without
limitation the following: (i) all registration and filing fees (including,
without limitation, fees and expenses (A) with respect to filings required to be
made with the Nasdaq and each other securities exchange or market on which
Registrable Securities are required hereunder to be listed, (B) with respect to
filings required to be made with the Commission, and (C) in compliance with
state securities or Blue Sky laws (including, without limitation, fees and
disbursements of one counsel for the Holders in connection with Blue Sky
qualifications of the Registrable Securities and determination of the
eligibility of the Registrable Securities for investment under the laws of such
jurisdictions as the Holders of a majority of Registrable Securities may
designate subject to the maximum fee of $2,500), (ii) printing expenses
(including, without limitation, expenses of printing certificates for
Registrable Securities and of printing prospectuses if the printing of
prospectuses is requested by the holders of a majority of the Registrable
Securities included in the Registration Statement), (iii) messenger, telephone
and delivery expenses, (iv) Securities Act liability insurance, if the Company
so desires such insurance, and (v) fees and expenses of all other Persons
retained by

                                      -8-
<PAGE>

the Company in connection with the consummation of the transactions contemplated
by this Agreement, including, without limitation, the Company's independent
public accountants (including the expenses of any comfort letters or costs
associated with the delivery by independent public accountants of a comfort
letter or comfort letters); provided that the Company shall not be responsible
for the fees and expenses of the Special Counsel. In addition, the Company shall
be responsible for all of its internal expenses incurred in connection with the
consummation of the transactions contemplated by this Agreement (including,
without limitation, all salaries and expenses of its officers and employees
performing legal or accounting duties), the expense of any annual audit, the
fees and expenses incurred in connection with the listing of the Registrable
Securities on any securities exchange as required hereunder.

     5.  Indemnification.
         ---------------

          (a)  Indemnification by the Company. The Company shall,
               ------------------------------
notwithstanding any termination of this Agreement, indemnify and hold harmless
each Holder, the officers, directors, agents, brokers (including brokers who
offer and sell Registrable Securities as principal as a result of a pledge or
any failure to perform under a margin call of Common Stock), investment advisors
and employees of each of them, each Person who controls any such Holder (within
the meaning of Section 15 of the Securities Act or Section 20 of the Exchange
Act) and the officers, directors, agents and employees of each such controlling
Person, and the respective successors, assigns, estate and personal
representatives of each of the foregoing, to the fullest extent permitted by
applicable law, from and against any and all claims, losses, damages,
liabilities, penalties, judgments, costs (including, without limitation, costs
of investigation) and expenses (including, without limitation, reasonable
attorneys' fees and expenses) (collectively, "Losses"), as incurred, arising
                                              ------
out of or relating to any untrue or alleged untrue statement of a material fact
contained in the Registration Statement, any Prospectus or any preliminary
prospectus or in any amendment or supplement thereto, or arising out of or
relating to any omission or alleged omission of a material fact required to be
stated therein or necessary to make the statements therein (in the case of any
Prospectus or preliminary prospectus or supplement thereto, in the light of the
circumstances under which they were made) not misleading, except to the extent,
but only to the extent, that such untrue statements or omissions are based
solely upon information regarding such Holder furnished in writing to the
Company by such Holder expressly for use therein, which information was
reasonably relied on by the Company for use therein or to the extent that such
information relates to such Holder or such Holder's proposed method of
distribution of Registrable Securities and was reviewed and expressly approved
in writing by such Holder expressly for use in the Registration Statement, such
Prospectus or such form of Prospectus or in any amendment or supplement thereto;
and provided, further, that with respect to any amended or supplemented
Prospectus, the foregoing indemnity agreement shall not apply or inure to the
benefit of any Holder from whom the Person asserting any Loss, purchased shares,
or any Person controlling such Holder, if, copies of an amended or supplemented
Prospectus were timely delivered to the Holder pursuant to this Agreement and a
copy of the Prospectus (as then amended or supplemented if the Company shall
have furnished any amendment or supplements thereto) was not sent or given by or
on behalf of such Holder to such Person, if required by law so to have been
delivered, and if the Prospectus (as so amended or supplemented) would have
cured the defect giving rise to such Loss. Such indemnity shall remain in full
force and effect regardless of any investigation made by or on behalf of an

                                      -9-
<PAGE>

Indemnified Party (as defined in Section 5(c) hereof) and shall survive the
transfer of the Registrable Securities by the Holders.

          (b)  Indemnification by Holders.  Each Holder shall, notwithstanding
               --------------------------
any termination of this Agreement, severally and not jointly, indemnify and hold
harmless the Company, and its directors, officers, agents and employees, each
Person who controls the Company (within the meaning of Section 15 of the
Securities Act and Section 20 of the Exchange Act), and the directors, officers,
agents or employees of such controlling Persons, and the respective successors,
assigns, estate and personal representatives of each of the foregoing, to the
fullest extent permitted by applicable law, from and against all Losses, as
incurred, arising out of, relating to, or based upon any untrue or alleged
untrue statement of a material fact contained in the Registration Statement, any
Prospectus, or any preliminary prospectus or in any amendment or supplement
thereto, or arising out of, relating to, or based upon any omission or alleged
omission of a material fact required to be stated therein or necessary to make
the statements therein (in the case of any Prospectus or preliminary prospectus
or supplement thereto, in the light of the circumstances under which they were
made) not misleading, to the extent, but only to the extent, that such untrue
statement or omission is contained in or omitted from any information so
furnished in writing by such Holder to the Company specifically for inclusion in
the Registration Statement or such Prospectus and that such information was
reasonably relied upon by the Company for use in the Registration Statement,
such Prospectus or such preliminary prospectus or to the extent that such
information relates to such Holder or such Holder's proposed method of
distribution of Registrable Securities and was reviewed and expressly approved
in writing by such Holder expressly for use in the Registration Statement, such
Prospectus or such preliminary Prospectus Supplement. Notwithstanding anything
to the contrary contained herein, the Holder shall be liable under this Section
5(b) for only that amount as does not exceed the net proceeds to such Holder as
a result of the sale of Registrable Securities pursuant to such Registration
Statement.

          (c)  Conduct of Indemnification Proceedings.  If any Proceeding shall
               --------------------------------------
be brought or asserted against any Person entitled to indemnity hereunder (an
"Indemnified Party"), such Indemnified Party promptly shall notify the
 ------------------
Person from whom indemnity is sought (the "Indemnifying Party) in writing, and
                                           ------------------
the Indemnifying Party shall assume the defense thereof, including the
employment of counsel reasonably satisfactory to the Indemnified Party and the
payment of all fees and expenses incurred in connection with defense thereof;
provided, that the failure of any Indemnified Party to give such notice shall
not relieve the Indemnifying Party of its obligations or liabilities pursuant to
this Agreement, except (and only) to the extent that it shall be finally
determined by a court of competent jurisdiction (which determination is not
subject to appeal or further review) that such failure shall have proximately
and materially adversely prejudiced the Indemnifying Party.

          An Indemnified Party shall have the right to employ separate counsel
in any such Proceeding and to participate in the defense thereof, but the fees
and expenses of such counsel shall be at the expense of such Indemnified Party
or Parties unless: (1) the Indemnifying Party has agreed in writing to pay such
fees and expenses; or (2) the Indemnifying Party shall have failed promptly to
assume the defense of such Proceeding and to employ counsel reasonably
satisfactory to such Indemnified Party in any such Proceeding; or (3) the named
parties to any such Proceeding (including any impleaded parties) include both
such Indemnified Party and the

                                      -10-
<PAGE>

Indemnifying Party, and such Indemnified Party shall have been advised by
counsel reasonably acceptable to the Indemnifying Party that a conflict of
interest is likely to exist if the same counsel were to represent such
Indemnified Party and the Indemnifying Party (in which case, if such Indemnified
Party notifies the Indemnifying Party in writing that it elects to employ
separate counsel at the expense of the Indemnifying Party, the Indemnifying
Party shall not have the right to assume the defense thereof on behalf of the
Indemnified Party and such counsel shall be at the expense of the Indemnifying
Party). The Indemnifying Party shall not be liable for any settlement of any
such Proceeding effected without its written consent, which consent shall not be
unreasonably withheld. No Indemnifying Party shall, without the prior written
consent of the Indemnified Party (which consent shall not be unreasonably
withheld), effect any settlement of any pending Proceeding in respect of which
any Indemnified Party is a party, unless such settlement includes an
unconditional release of such Indemnified Party from all liability on claims
that are the subject matter of such Proceeding.

          All fees and expenses of the Indemnified Party (including reasonable
fees and expenses to the extent incurred in connection with investigating or
preparing to defend such Proceeding in a manner not inconsistent with this
Section) shall be paid to the Indemnified Party, as incurred, within ten (10)
Business Days of written notice thereof to the Indemnifying Party (regardless of
whether it is ultimately determined that an Indemnified Party is not entitled to
indemnification hereunder; provided, that the Indemnifying Party may require
                           --------
such Indemnified Party to undertake to reimburse all such fees and expenses to
the extent it is finally judicially determined that such Indemnified Party is
not entitled to indemnification hereunder).

          (d)  Contribution. If a claim for indemnification under Section 5(a)
               ------------
or 5(b) is unavailable to an Indemnified Party because of a failure or refusal
of a governmental authority to enforce such indemnification in accordance with
its terms (by reason of public policy or otherwise), then each Indemnifying
Party, in lieu of indemnifying such Indemnified Party, shall contribute to the
amount paid or payable by such Indemnified Party as a result of such Losses, in
such proportion as is appropriate to reflect the relative fault of the
Indemnifying Party and Indemnified Party in connection with the actions,
statements or omissions that resulted in such Losses as well as any other
relevant equitable considerations. The relative fault of such Indemnifying Party
and Indemnified Party shall be determined by reference to, among other things,
whether any action in question, including any untrue or alleged untrue statement
of a material fact or omission or alleged omission of a material fact, has been
taken or made by, or relates to information supplied by, such Indemnifying,
Party or Indemnified Party, and the parties' relative intent, knowledge, access
to information and opportunity to correct or prevent such action, statement or
omission. The amount paid or payable by a party as a result of any Losses shall
be deemed to include, subject to the limitations set forth in Section 5(c), any
reasonable attorneys' or other reasonable fees or expenses incurred by such
party in connection with any Proceeding to the extent such party would have been
indemnified for such fees or expenses if the indemnification provided for in
this Section was available to such party in accordance with its terms.
Notwithstanding anything to the contrary contained herein, the Holder shall be
liable or required to contribute under this Section 5(c) for only that amount as
does not exceed the net proceeds to such Holder as a result of the sale of
Registrable Securities pursuant to such Registration Statement.

                                      -11-
<PAGE>

          The parties hereto agree that it would not be just and equitable if
contribution pursuant to this Section 5(d) were determined by pro rata
allocation or by any other method of allocation that does not take into account
the equitable considerations referred to in the immediately preceding paragraph.
No Person guilty of fraudulent misrepresentation (within the meaning of Section
11(f) of the Securities Act) shall be entitled to contribution from any Person
who was not guilty of such fraudulent misrepresentation.

          The indemnity and contribution agreements contained in this Section
are in addition to any liability that the Indemnifying Parties may have to the
Indemnified Parties

     6.   Rule 144.
          --------

          As long as any Holder owns Registrable Securities the Company
covenants to timely file (or obtain extensions in respect thereof and file
within the applicable grace period) all reports required to be filed by the
Company after the date hereof pursuant to Section 13(a) or 15(d) of the Exchange
Act and to promptly furnish the Holders with true and complete copies of all
such filings.  As long as any Holder owns Registrable Securities, if the Company
is not required to file reports pursuant to Section 13(a) or 15(d) of the
Exchange Act, it will prepare and furnish to the Holders and make publicly
available in accordance with Rule 144(c) promulgated under the Securities Act
annual and quarterly financial statements, together with a discussion and
analysis of such financial statements in form and substance substantially
similar to those that would otherwise be required to be included in reports
required by Section 13(a) or 15(d) of the Exchange Act, as well as any other
information required thereby, in the time period that such filings would have
been required to have been made under the Exchange Act.  The Company further
covenants that it will take such further action as any Holder may reasonably
request, all to the extent required from time to time to enable such Person to
sell Common Stock without registration under the Securities Act within the
limitation of the exemptions provided by Rule 144 promulgated under the
Securities Act, including providing any legal opinions of counsel to the Company
referred to in the Purchase Agreement.  Upon the request of any Holder, the
Company shall deliver to such Holder a written certification of a duly
authorized officer as to whether it has complied with such requirements.

     7.   Miscellaneous.
          -------------
          (a)  Remedies.  In the event of a breach by the Company or by a
               --------
Holder, of any of their obligations under this Agreement, each Holder or the
Company, as the case may be, in addition to being entitled to exercise all
rights granted by law and under this Agreement, including recovery of damages,
will be entitled to specific performance of its rights under this Agreement. The
Company and each Holder agree that monetary damages would not provide adequate
compensation for any losses incurred by reason of a breach by it of any of the
provisions of this Agreement and hereby further agrees that, in the event of any
action for specific performance in respect of such breach, it shall waive the
defense that a remedy at law would be adequate.

          (b)  No Inconsistent Agreements.  Neither the Company nor any of its
               --------------------------
subsidiaries has, as of the date hereof entered into and currently in effect,
nor shall the Company or any of its subsidiaries, on or after the date of this
Agreement, enter into any agreement with

                                      -12-
<PAGE>

respect to its securities that is inconsistent with the rights granted to the
Holders in this Agreement or otherwise conflicts with the provisions hereof.
Except as disclosed in the Commission Documents, neither the Company nor any of
its subsidiaries has previously entered into any agreement currently in effect
granting any registration rights with respect to any of its securities to any
Person. Without the written consent of the Holders of a majority of the then
outstanding Registrable Securities, the Company shall not grant to any Person
the right to request the Company to register any securities of the Company under
the Securities Act unless the rights so granted are subject in all respects to
the prior rights in full of the Holders set forth herein, and are not otherwise
in conflict with the provisions of this Agreement.

          (c)  Piggy-Back Registrations. If at any time during the Effectiveness
               ------------------------
Period when there is not an effective Registration Statement covering Common
Shares, the Company shall determine to prepare and file with the Commission a
registration statement relating to an offering for its own account or the
account of others under the Securities Act of any of its equity securities,
other than on Form S-4 or Form S-8 (each as promulgated under the Securities
Act) or its then equivalents relating to equity securities to be issued solely
in connection with any acquisition of any entity or business or equity
securities issuable in connection with stock option or other employee benefit
plans, the Company shall send to each holder of Registrable Securities written
notice of such determination and, if within ten (10) days after receipt of such
notice, any such holder shall so request in writing (which request shall specify
the Registrable Securities intended to be disposed of by the Holders), the
Company will use its best efforts to cause the registration under the Securities
Act of all Registrable Securities which the Company has been so requested to
register by the holder, to the extent requisite to permit the disposition of the
Registrable Securities so to be registered, provided that if at any time after
giving written notice of its intention to register any securities and prior to
the effective date of the registration statement filed in connection with such
registration, the Company shall determine for any reason not to register or to
delay registration of such securities, the Company may, at its election, give
written notice of such determination to such holder and, thereupon, (i) in the
case of a determination not to register, shall be relieved of its obligation to
register any Registrable Securities in connection with such registration (but
not from its obligation to pay expenses in accordance with Section 4 hereof),
and (ii) in the case of a determination to delay registering, shall be permitted
to delay registering any Registrable Securities being registered pursuant to
this Section 7(d) for the same period as the delay in registering such other
securities. The Company shall include in such registration statement all or any
part of such Registrable Securities such holder requests to be registered;
provided, however, that the Company shall not be required to register any
--------  -------
Registrable Securities pursuant to this Section 7(d) that are eligible for sale
pursuant to Rule 144(k) of the Securities Act. In the case of an underwritten
public offering, if the managing underwriter(s) or underwriter(s) should
reasonably object to the inclusion of the Registrable Securities in such
registration statement, then if the Company after consultation with the managing
underwriter should reasonably determine that the inclusion of such Registrable
Securities, would materially adversely affect the offering contemplated in such
registration statement, and based on such determination recommends inclusion in
such registration statement of fewer or none of the Registrable Securities of
the Holders, then (x) the number of Registrable Securities of the Holders
included in such registration statement shall be reduced pro-rata among such
Holders (based upon the number of Registrable Securities requested to be
included in the registration), if the Company after consultation with the
underwriter(s) recommends the inclusion of fewer Registrable Securities, or (y)
none of the Registrable Securities of the Holders

                                      -13-
<PAGE>

shall be included in such registration statement, if the Company after
consultation with the underwriter(s) recommends the inclusion of none of such
Registrable Securities.

          (d)  Failure to File Registration Statement and Other Events. The
               -------------------------------------------------------
Company and the Holders agree that the Holders will suffer damages if the
Registration Statement is not filed or confidentially submitted on or prior to
the Filing Date and not declared effective by the Commission on or prior to the
Effectiveness Date and maintained in the manner contemplated herein during the
Effectiveness Period or if certain other events occur. The Company and the
Holders further agree that it would not be feasible to ascertain the extent of
such damages with precision. Accordingly, if (I) the Registration Statement is
not filed or confidentially submitted on or prior to the Filing Date, or is not
declared effective by the Commission on or prior to the Effectiveness Date (or
in the event an additional Registration Statement is filed or confidentially
submitted because the actual number of Common Shares exceeds the number of
shares of Common Shares initially registered is not filed and declared effective
within the time periods set forth in Section 2), or (II) the Company fails to
file with the Commission a request for acceleration in accordance with Rule 12d
l-2 promulgated under the Exchange Act within five (5) days of the date that the
Company is notified (orally or in writing, whichever is earlier) by the
Commission that a Registration Statement will not be "reviewed," or not subject
to further review, or (III) the Registration Statement is filed with and
declared effective by the Commission but thereafter ceases to be effective as to
all Registrable Securities at any time prior to the expiration of the
Effectiveness Period, without being succeeded by a subsequent Registration
Statement filed with and declared effective by the Commission, or (IV) trading
in the Common Stock shall be suspended for any reason for more than three (3)
Business Days in the aggregate, or (V) the Company has breached Section 3(n) of
this Agreement (any such failure or breach being referred to as an "Event"), the
                                                                    -----
Company shall pay in cash as liquidated damages for such failure and not as a
penalty (the "Liquidated Damages") to each Holder an amount equal to 2% of the
              ------------------
aggregate purchase price of all of the Registrable Securities then held by such
Holder for each thirty (30) day period following such Event until the applicable
Event has been cured, which amount shall be pro rated for any periods less than
thirty (30) days (the "Periodic Amount"). Payments to be made pursuant to this
                       ---------------
Section 7(d) shall be due and payable immediately upon demand at the option of
the Holders in cash. The parties agree that the Periodic Amount represents a
reasonable estimate on the part of the parties, as of the date of this
Agreement, of the amount of damages that may be incurred by the Holders if the
Registration Statement is not filed on or prior to the Filing Date or has not
been declared effective by the Commission on or prior to the Effectiveness Date
and maintained in the manner contemplated herein during the Effectiveness Period
or if any other Event as described herein has occurred.

          (e)  Specific Enforcement, Consent to Jurisdiction.
               ---------------------------------------------

               (i)  The Company and the Holders acknowledge and agree that
irreparable damage would occur in the event that any of the provisions of this
Registration Rights Agreement or the Purchase Agreement were not performed in
accordance with their specific terms or were otherwise breached. It is
accordingly agreed that the parties shall be entitled to enforce specifically
the terms and provisions of the registration rights agreement or the purchase
agreement; provided, however, that with respect to any provision with respect
           --------  -------
to which the Buyer entitled to receive Liquidated Damages, the sole remedy of
the Buyer will be to enforce specifically its right to receive such Liquidated
Damages.

                                      -14-
<PAGE>

               (ii) Both the Company and the Purchaser (i) hereby irrevocably
submits to the jurisdiction of the United States District Court for the Southern
District of New York and the courts of the State of New York located in New York
county for the purposes of any suit, action or proceeding arising out of or
relating to this Agreement or the Purchase Agreement and (ii) hereby waives, and
agrees not to assert in any such suit, action or proceeding, any claim that it
is not personally subject to the jurisdiction of such court, that the suit,
action or proceeding is brought in an inconvenient forum or that the venue of
the suit, action or proceeding is improper. Both the Company and the Purchaser
consents to process being served in any such suit, action or proceeding by
mailing a copy thereof to such party at the address in effect for notices to it
under this Agreement and agrees that such service shall constitute good and
sufficient service of process and notice thereof. Nothing in this Section 7(e)
shall affect or limit any right to serve process in any other manner permitted
by law.

          (f)  Amendments and Waivers. The provisions of this Agreement,
               ----------------------
including the provisions of this sentence, may not be amended, modified or
supplemented, and waivers or consents to departures from the provisions hereof
may not be given, unless the same shall be in writing and signed by the Company
and each of the Holders. Notwithstanding the foregoing, a waiver or consent to
depart from the provisions hereof with respect to a matter that relates
exclusively to the rights of Holders and that does not directly or indirectly
affect the rights of other Holders may be given by Holders of at least a
majority of the Registrable Securities to which such waiver or consent relates;
provided, however, that the provisions of this sentence may not be amended,
--------  -------
modified, or supplemented except in accordance with the provisions of the
immediately preceding sentence.

          (g)  Notices. Any and all notices or other communications or
               -------
deliveries required or permitted to be provided hereunder shall be in writing
and shall be deemed to have been duly given: when delivered by hand, if
personally delivered; when receipt is acknowledged, if telecopied; or when
actually received or refused if sent by other means.

               (x)  if to the Company:

                    Myriad Genetics Inc.
                    320 Wakara Way
                    Salt Lake City, Utah 84108
                    Tel. No.: (801) 584-3600
                    Fax No.: (801) 584-3640
                    Attn: President

                    with a copy to:

                    Lewis J. Geffen, Esq.
                    Mintz Levin Cohn Ferris Glovsky and Popeo PC
                    One Financial Center
                    Boston, Massachusetts 02111
                    Tel. No.: (617) 542-6000
                    Fax No.:  (617) 542-2241

                                      -15-
<PAGE>

               (y)  if to the Purchaser:

                    Acqua Wellington North American Equities Fund, Ltd.
                    c/o Fortis Fund Services (Bahamas) Ltd.
                    Montague Sterling Centre
                    East Bay Street, P. O. Box SS-6238
                    Nassau, Bahamas
                    Tel. No.: (242) 394-2700
                    Fax No.: (242) 394-9667
                    Attention:  Anthony L.M. Inder Rieden

or to such other address or addresses or facsimile number or numbers as any such
party may most recently have designated in writing to the other parties hereto
by such notice.

          (h)  Successors and Assigns. This Agreement shall be binding upon and
               ----------------------
inure to the benefit of the parties and their successors and permitted assigns
and shall inure to the benefit of each Holder and its successors and assigns.
The Company may not assign this Agreement or any of its rights or obligations
hereunder without the prior written consent of each Holder which consent will
not be unreasonably withheld. Each Purchaser may assign its rights hereunder in
the manner and to the Persons as permitted under the Purchase Agreement.

          (i)  Assignment of Registration Rights. The rights of each Holder
               ---------------------------------
hereunder, including the right to have the Company register for resale
Registrable Securities in accordance with the terms of this Agreement, shall be
automatically assignable by each Holder to any transferee of such Holder of all
or at least 50,000 shares of Registrable Securities if: (i) the Holder agrees in
writing with the transferee or assignee to assign such rights, and a copy of
such agreement is furnished to the Company within a reasonable time after such
assignment, (ii) the Company is, within a reasonable time after such transfer or
assignment, furnished with written notice of (a) the name and address of such
transferee or assignee, and (b) the securities with respect to which such
registration rights are being transferred or assigned, (iii) following such
transfer or assignment the further disposition of such securities by the
transferee or assignees is restricted under the Securities Act and applicable
state securities laws, (iv) at or before the time the Company receives the
written notice contemplated by clause (ii) of this Section, the transferee or
assignee agrees in writing (in form and substance reasonably satisfactory to the
Company) with the Company to be bound by all of the provisions of this
Agreement, and (v) such transfer shall have been made in accordance with the
applicable requirements of the Purchase Agreement. In addition, each Holder
shall have the right to assign its rights hereunder to any other Person with the
prior written consent of the Company, which consent shall not be unreasonably
withheld. The rights to assignment shall apply to the Holders (and to
subsequent) successors and assigns.

          (j)  Counterparts.  This Agreement may be executed in any number of
               ------------
counterparts, each of which when so executed shall be deemed to be an original
and, all of which taken together shall constitute one and the same Agreement. In
the event that any signature is delivered by facsimile transmission, such
signature shall create a valid binding obligation of the

                                      -16-
<PAGE>

party executing (or on whose behalf such signature is executed) the same with
the same force and effect as if such facsimile signature were the original
thereof.

          (k)  Governing Law. This Agreement shall be governed by and construed
               -------------
in accordance with the laws of the State of New York, without regard to
principles of conflicts of law thereof. This Agreement shall not be interpreted
or construed with any presumption against the party causing this Agreement to be
drafted.

          (l)  Severability. If any term, provision, covenant or restriction of
               ------------
this Agreement is held to be invalid, illegal, void or unenforceable in any
respect, the remainder of the terms, provisions, covenants and restrictions set
forth herein shall remain in full force and effect and shall in no way be
affected, impaired or invalidated, and the parties hereto shall use their
reasonable efforts to find and employ an alternative means to achieve the same
or substantially the same result as that contemplated by such term, provision,
covenant or restriction. It is hereby stipulated and declared to be the
intention of the parties that they would have executed the remaining terms,
provisions, covenants and restrictions without including any of such that may be
hereafter declared invalid, illegal, void or unenforceable.

          (m)  Headings. The headings herein are for convenience only, do not
               --------
constitute a part of this Agreement and shall not be deemed to limit or affect
any of the provisions hereof.

                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                      -17-
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have caused this Registration
Rights Agreement to be duly executed by their respective authorized persons as
of the date first indicated above.

                              MYRIAD GENETICS INC.

                              By:  /s/ Peter D. Meldrum
                              ----------------------------------------------
                                   Name: Peter D. Meldrum
                                   Title:  President and C.E.O.

                              ACQUA WELLINGTON NORTH AMERICAN EQUITIES FUND,
                              LTD.

                              By:  /s/ Helen A. Forbes
                              ----------------------------------------------
                                   Name:  Helen A. Forbes
                                   Title:  Secretary

                                      -18-

<PAGE>

                                                                       EXHIBIT A

                        FORM OF NOTICE OF EFFECTIVENESS
                           OF REGISTRATION STATEMENT

[TRANSFER AGENT]
[ADDRESS]

Attn:  _____________

          Re:  Myriad Genetics Inc.
               --------------------

Ladies and Gentlemen:

     We are counsel to Myriad Genetics Inc., a Delaware corporation (the
"Company"), and have represented the Company in connection with that certain
Common Stock Purchase Agreement (the "Purchase Agreement"), dated as of October
__, 2000, by and between the Company and the Purchaser named therein pursuant to
which the Company issued to the Purchaser shares (the "Common Stock") of its
Common Stock, no par value (the "Common Stock").  Pursuant to the Purchase
Agreement, the Company has also entered into a Registration Rights Agreement
with the Purchaser (the "Registration Rights Agreement"), dated as of October
__, 2000, pursuant to which the Company agreed, among other things, to register
the Registrable Securities (as defined in the Registration Rights Agreement),
including the Common Stock, under the Securities Act of 1933, as amended (the
"1933 Act").  In connection with the Company's obligations under the
Registration Rights Agreement, on ________________, 2000, the Company filed a
Registration Statement on Form ___ (File No. 333-________) (the "Registration
Statement") with the Securities and Exchange Commission (the "SEC") relating to
the resale of the Registrable Securities which names each of the present Holders
as a selling stockholder thereunder.

     In connection with the foregoing, we advise you that a member of the SEC's
staff has advised us by telephone that the SEC has entered an order declaring
the Registration Statement effective under the 1933 Act at [ENTER TIME OF
EFFECTIVENESS] on [ENTER DATE OF EFFECTIVENESS] and we have no knowledge that
any stop order suspending its effectiveness has been issued or that any
proceedings for that purpose are pending before, or threatened by, the SEC and,
accordingly, the Registrable Securities are available for resale under the 1933
Act in the manner specified in, and pursuant to the terms of the Registration
Statement for so long as such Registration Statement remains effective and
current.

                                    Very truly yours,

                                    By:

cc:  Acqua Wellington North American Equities, Ltd.<PAGE>

                                Exhibit 10.29.

    Seventh Amendment to the Loan Agreement with Chase Bank of Texas, N.A.
<PAGE>

                                                                   Exhibit 10.29

                      SEVENTH AMENDMENT TO LOAN AGREEMENT
                      -----------------------------------

     This SEVENTH AMENDMENT TO LOAN AGREEMENT (this "Amendment"). dated as of
                                                     -----------
January 28, 2000, is among SONIC CORP., a Delaware corporation (the "Borrower"),
                                                                     --------
each of the banks or other lending institutions which is or may from time to
time become a signatory or party to the Agreement (hereinafter defined) or any
successor or permitted assignee thereof (each a "Bank" and collectively, the
                                                 ----
"Banks"), and CHASE BANK OF TEXAS, NATIONAL ASSOCIATION (formerly known as Texas
------
Commerce Bank National Association), a national banking association ("Chase"),
                                                                      -----
as agent for itself and the other Banks and as issuer of Letters of Credit under
the Agreement (in such capacity, together with its successors in such capacity,
the "Agent").
     -----

                                   RECITALS:

     A.  Borrower, Agent and Banks have entered into that certain Loan Agreement
dated as of July 12, 1995, as amended by (i) that certain First Amendment to
Loan Agreement dated as of August 16, 1996, (ii) that certain Second Amendment
to Loan Agreement dated as of September 27, 1996, (iii) that certain Third
Amendment to Loan Agreement dated as of June 19, 1997, (iv) that certain Fourth
Amendment to Loan Agreement dated as of January 27, 1998, (v) that certain Fifth
Amendment to Loan Agreement dated as of April 2, 1998, and (vi) that certain
Sixth Amendment to Loan Agreement dated as of June 2, 1999 (as amended, the
"Agreement").
----------

     B.  Pursuant to the Agreement, the undersigned guarantors (each a
"Guarantor" and, collectively, the "Guarantors") have executed Guaranties which
----------                          ----------
guarantee to Agent the payment and performance of the Obligations.

     C.  Borrower, Agent and Banks now desire to amend the Agreement to extend
the Termination Date, as provided herein.

     NOW, THEREFORE, in consideration of the premises herein contained and other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

                                   ARTICLE I

                                  Definitions
                                  -----------

     Section 1.1  Definitions. Capitalized terms used in this Amendment, to the
                  -----------
extent no otherwise defined herein, shall have the same meanings as in the
Agreement, as amended hereby.
<PAGE>

                                   ARTICLE II

                                   Amendments
                                   ----------

     Section 2.1  Amendment to Termination Date. Effective as of the date
                  -----------------------------
hereof, the definition of "Termination Date" appearing in Section 1.1 of the
Agreement is hereby amended to read in its entirety as follows:

          "Termination Date" means the earlier of (a) 11:00 a.m. Dallas, Texas
           ----------------
     time on July 12, 2002 or such later date to which the Termination Date may
     be extended pursuant to Section 2.11, or (b) such earlier date on which the
     Commitments terminate as provided in this Agreement.

                                  ARTICLE III

                              Conditions Precedent
                              --------------------

     Section 3.1  Conditions. The effectiveness of this Amendment is subject to
                  ----------
the satisfaction of each of the following conditions precedent:

     (a) Representations and Warranties. The representations and warranties
         ------------------------------
contained herein and in all other Loan Documents, as amended hereby, shall be
true and correct as of the date hereof as if made on the date hereof;

     (b) No Default. No Event of Default shall have occurred and be continuing
         ----------
and no event or condition shall have occurred that with the giving of notice or
lapse of time or both would be an Event of Default; and

     (c) Corporate Matters. All corporate proceedings taken in connection with
         -----------------
the transactions contemplated by this Amendment and all documents, instruments,
and other legal matters incident thereto shall be satisfactory to Agent and its
legal counsel, Winstead Sechrest & Minick P.C.

                                   ARTICLE IV

                 Ratifications, Representations and Warranties
                 ---------------------------------------------

  Section 4.1  Ratifications. The terms and provisions set forth in this
               -------------
Amendment shall modify and supersede all inconsistent terms and provisions set
forth in the Agreement and except
<PAGE>

as expressly modified and superseded by this Amendment, the terms and provisions
of the Agreement are ratified and confirmed and shall continue in full force and
effect. Borrower, Agent and the Banks agree that the Agreement as amended hereby
shall continue to be legal, valid, binding and enforceable in accordance with
its terms.

     Section 4.2  Release of Claims. The Borrower and the Guarantors each hereby
                  -----------------
acknowledge and agree that to their knowledge none of them has any and there are
no claims or offsets against or defenses or counterclaims to the terms and
provisions of or the obligations of the Borrower, any Guarantor or any
Subsidiary created or evidenced by the Agreement or any of the other Loan
Documents, and to the extent any such claims, offsets, defenses or counterclaims
exist, the Borrower and the Guarantors each hereby waive, and hereby release the
Agent and each of the Banks from, any and all claims, offsets, defenses and
counterclaims that are known to the Borrower or any Guarantor as of the date
hereof, such waiver and release being with full knowledge and understanding of
the circumstances and effects of such waiver and release and after having
consulted legal counsel with respect thereto.

     Section 4.3  Representations and Warranties. Borrower hereby represents and
                  ------------------------------
warrants to Agent and the Banks that (i) the execution, delivery and performance
of this Amendment and any and all other Loan Documents executed and/or delivered
in connection herewith have been authorized by all requisite corporate,
partnership and trust action on the part of Borrower and the Guarantors and will
not violate the articles of incorporation, bylaws, partnership agreement or
other organizational documents of Borrower or the Guarantors, (ii) the
representations and warranties contained in the Agreement, as amended hereby,
and any other Loan Document are true and correct on and as of the date hereof as
though made on and as of the date hereof, (iii) no Event of Default has occurred
and is continuing and no event or condition has occurred that with the giving of
notice or lapse of time or both would be an Event of Default, and (iv) Borrower
is in full compliance with all covenants and agreements contained in the
Agreement as amended hereby.

                                   ARTICLE V

                                 Miscellaneous
                                 -------------

     Section 5.1  Survival of Representations and Warranties. All
                  ------------------------------------------
representations and warranties made in this Amendment or any other Loan Document
including any Loan Document furnished in connection with this Amendment shall
survive the execution and delivery of this Amendment and the other Loan
Documents, and no investigation by Agent or any Bank or any closing shall affect
the representations and warranties or the right of Agent and the Banks to rely
upon them.

     Section 5.2  Reference to Agreement. Each of the Loan Documents, including
                  ----------------------
the Agreement and any and all other agreements, documents, or instruments now or
hereafter executed and delivered pursuant to the terms hereof or pursuant to the
terms of the Agreement as
<PAGE>

amended hereby, are hereby amended so that any reference in such Loan Documents
to the Agreement shall mean a reference to the Agreement as amended hereby.

     Section 5.3  Expenses of Agent. As provided in the Agreement, Borrower
                  -----------------
agrees to pay on demand all reasonable costs and expenses incurred by Agent in
connection with the preparation, negotiation, and execution of this Amendment
and the other Loan Documents executed pursuant hereto and any and all
amendments, modifications, and supplements thereto, including without limitation
the reasonable costs and fees of Agent's legal counsel.

     Section 5.4  Severability. Any provision of this Amendment held by a court
                  ------------
of competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

     Section 5.5  APPLICABLE LAW. THIS AMENDMENT AND ALL OTHER LOAN DOCUMENTS
                  --------------
EXECUTED PURSUANT HERETO SHALL BE DEEMED TO HAVE BEEN MADE AND TO BE PERFORMABLE
IN DALLAS, DALLAS COUNTY, TEXAS AND SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS.

     Section 5.6  Successors and Assigns. This Amendment is binding upon and
                  ----------------------
shall inure to the benefit of Borrower, Agent and the Banks and their respective
successors and permitted assigns, except Borrower may not assign or transfer any
of its rights or obligations hereunder without the prior written consent of
Agent.

     Section 5.7  Counterparts. This Amendment may be executed in one or more
                  ------------
counterparts, each of which when so executed shall be deemed to be an original,
but all of which when taken together shall constitute one and the same
instrument.
<PAGE>

     Section 5.8   Effect of Waiver. No consent or waiver, express or implied,
                   ----------------
by Agent or any Bank to or for any breach of or deviation from any covenant,
condition or duty by Borrower or any Guarantor shall be deemed a consent or
waiver to or of any other breach of the same or any other covenant, condition or
duty.

     Section 5.9   Headings. The headings, captions, and arrangements used in
                   --------
this Amendment are for convenience only and shall not affect the interpretation
of this Amendment.

     Section 5.10  Non-Application of Chapter 346 of Texas Finance Code. The
                   ----------------------------------------------------
provisions of Chapter 346 of the Texas Finance Code (formerly Chapter 15 of the
Texas Credit Code (Vernon's Annotated Texas Statutes, Article 5069-15)), as
amended, are specifically declared by the parties not to be applicable to this
Amendment or any of the Loan Documents or the transactions contemplated hereby.

     Section 5.11  ENTIRE AGREEMENT. THIS AMENDMENT AND ALL OTHER INSTRUMENTS,
                   ----------------
DOCUMENTS AND AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH THIS
AMENDMENT EMBODY THE FINAL, ENTIRE AGREEMENT AMONG THE PARTIES HERETO REGARDING
THIS AMENDMENT AND SUPERSEDE ANY AND ALL PRIOR COMMITMENTS, AGREEMENTS,
REPRESENTATIONS AND UNDERSTANDINGS, WHETHER WRITTEN OR ORAL, RELATING TO THIS
AMENDMENT, AND MAY NOT BE CONTRADICTED OR VARIED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OR DISCUSSIONS OF THE PARTIES
HERETO. THERE ARE NO ORAL AGREEMENTS AMONG THE PARTIES HERETO.

     Executed as of the date first written above.

                                   BORROWER:
                                   --------

                                  SONIC CORP.

                             By: /s/ W. Scott McLain
                                --------------------------------
                                W. Scott McLain
                                Chief Financial Officer
<PAGE>

                         AGENTS AND BANKS:
                         -----------------

                         CHASE BANK OF TEXAS, NATIONAL
                         ASSOCIATION (formerly known as Texas
                         Commerce Bank National Association), as Agent
                         and as a Bank.

                         By:
                         /s/ Kara J. Nordstrom
                            --------------------------------------------
                             Name:  Kara J. Nordstrom
                                  --------------------------------------
                             Title: Vice President
                                   -------------------------------------

                         BANK OF AMERICA, N.A. (formerly Nations
                         Bank, N.A., formerly Boatmen's National Bank of
                         Oklahoma, formerly Bank IV Oklahoma, N.A.)

                         By:/s/ Michael S. Reeves
                            --------------------------------------------
                             Name:         Michael S. Reeves
                                   -------------------------------------
                             Title:    Senior Vice President
--                                  ------------------------------------

                         UMB OKLAHOMA BANK

                         By:/s/ Richard J. Lehrter
                            --------------------------------------------
                             Name:  Richard J. Lehrter
                                   -------------------------------------
                             Title: Executive Vice President
                                    ------------------------------------

                         SUMMIT BANK

                         By:/s/ Catherine E. Farrity
                            --------------------------------------------
                             Name:   Catherine E. Farrity
                                  --------------------------------------
                             Title: Vice President
                                   -------------------------------------

                         BANCFIRST

                         By:/s/ Brian K. Rewz
                            --------------------------------------------
                             Name:   Brian K. Rewz
                                  --------------------------------------
                             Title: Senior Vice President
                                   -------------------------------------
<PAGE>

Each Guarantor hereby (a) consents and agrees to this Amendment, (b) agrees that
its respective Guaranty shall continue to by the legal, valid and binding
obligation of such Guarantor enforceable against such Guarantor in accordance
with its terms, and (c) represents and warrants that each of the representations
and warranties set forth in this Amendment with regard to each such Guarantor
are true and correct in all respects.

                              GUARANTORS:
                              -----------

                              SONIC RESTAURANTS, INC.

                              By:/s/ W. Scott McLain
                                 -------------------------------------
                                     Name: W. Scott McLain
                                          ----------------------------
                                     Title:  Chief Financial Officer
                                           ---------------------------

                              SONIC INDUSTRIES  INC.

                              By:/s/ W. Scott McLain
                                 -------------------------------------
                                     Name:  W. Scott McLain
                                         -----------------------------
                                     Title:  Chief Financial Officer
                                          ----------------------------

                              AMERICA'S DRIVE-IN CORP.

                              By:/s/ W. Scott McLain
                                 -------------------------------------
                                     Name:   W. Scott McLain
                                          ----------------------------
                                     Title: Chief Financial Officer
                                           ---------------------------

                              AMERICA'S DRIVE-IN TRUST

                              By:/s/ W. Scott McLain
                                 -------------------------------------
                                     Name:   W. Scott McLain
                                          ----------------------------
                                     Title:  Chief Financial Officer
                                            --------------------------
<PAGE>

                              EACH OF THE PARTNERSHIPS SPECIFIED ON
                              ANNEX 1 HERETO, each an Oklahoma general
                              partnership

                              By:  Sonic Restaurants, Inc.,
                                             Managing General Partner of
                                             each of such partnerships

                                   By:/s/ W. Scott McLain
                                      ------------------------------------
                                      W. Scott McLain
                                           Chief Financial Officer
<PAGE>

                                    ANNEX 1

                                 Partnerships
                                 ------------

                 [List of Partnerships Intentionally Omitted]

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