<PAGE>   1
                                                 Drager/Aspect Product Agreement
                                                         Drager-Aspect Vers1.doc
                                                                        20.04.99

                                                                    Exhibit 10.6


                          Aspect Medical Systems, Inc.
has requested that the marked portions of this agreement be granted confidential
  treatment pursuant to Rule 406 under the Securities Act of 1933, as amended.

                         Drager/Aspect Product Agreement



                                     between

                          Aspect Medical Systems, Inc.
                                 2 Vision Drive
                                     Natick
                                  MA 01760-2059
                                       USA

                         - hereinafter called "Aspect" -


                                       and

                           Drager Medizintechnik GmbH
                            Moislinger Allee 53 - 55
                                  23558 Lubeck
                                     Germany
                         - hereinafter called "Drager" -

         - Aspect and Drager together hereinafter called "the Parties" -


<PAGE>   2
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                      - 2 -

     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

Whereas Aspect has a long-standing tradition of designing, manufacturing and
distributing neuromonitors including the BIS (Bispectral Index) and Sensors for
neuromonitors.


Whereas Drager has a long-standing tradition of designing, manufacturing and
distributing medical equipment.


Whereas Drager is in the process of designing a new anesthesia workplace.


Whereas Drager wishes to integrate Aspect's BIS technology and to offer a
Drager-BIS-Module as an option into this and other workplace solutions for the
[**] and [**]


Whereas Aspect desires to sell and Drager desires to purchase, on the terms and
conditions set forth below in this Agreement, certain quantities of Aspect BIS
Module Kits and the required Sensors manufactured by Aspect.

Now, therefore,

in consideration of the mutual covenants, terms and conditions hereinafter
expressed, the Parties agree as follows:

1.       DEFINITIONS

1.1      The term "Aspect BIS Module Kits" shall mean Aspect's BIS Module Kits
         as further defined in the specifications in Exhibit A.

         The Parties hereto may change Exhibit A, to the extent it may then be
         necessary to reflect a subsequent modification made pursuant to Clause
         7 of this Agreement.

1.2      The term "Drager-BIS-Module" shall mean an Aspect BIS Module Kit that
         is integrated by Drager into a Drager Workplace.


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                                                 Drager/Aspect Product Agreement
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                                      - 3 -

     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

1.3      The term "Aspect BIS Sensor" shall mean a single use disposable sensor
         for the use with the Aspect BIS Module Kits or the Aspect stand-alone
         BIS monitor.

1.4      The term [**] shall mean a [**] that has been [**] in accordance with
         [**] to [**] with the [**] Drager shall own all right, title, and
         interest in any modifications (the "[**]" made to the [**] to [**] the
         [**] for use in the [**]. The [**] will [**] Aspect BIS Module Kits
         sold by Aspect [**]. The [**] may [**] in [**] depending upon
         negotiations between the Parties (See Exhibit A, Section 1.5).

1.5      The term "Products" shall mean the Aspect BIS Module Kits, the
         Drager-BIS-Modules, the Aspect's BIS Sensors,[**].

1.6      The term "Drager Workplace" shall mean a combination of devices for
         [**] and [**] with a [**] and [**] to all [**]. The definition Drager
         Workplace includes a [**] and a [**] for [**].

2.       DRAGER'S RIGHTS TO PURCHASE AND SELL AND ASPECT'S RESPONSIBILITIES

2.1      Drager shall have the non-exclusive right during the term of this
         Agreement to purchase the Aspect BIS Module Kit for the sole purpose of
         integrating the Aspect BIS Module Kit into a Drager Workplace and
         reselling the finished Drager-BIS-Module worldwide.

         Subject to Clause 2.2 Drager shall have the exclusive right during the
         term of this Agreement to purchase the [**] for the [**] of [**] the
         [**] except in the USA. Aspect shall not have the right to manufacture
         or distribute the [**] to [**].

         Drager shall have the non-exclusive right during the term of this
         Agreement to purchase the Aspect BIS Sensor for the non-exclusive
         resale worldwide except in the USA.

2.2      Drager will sell the Drager-BIS-Module, the [**] and the Aspect BIS
         Sensor through its designated distribution network, and Aspect shall
         not with respect to the Drager-BIS-Module and the [**] make any sales
         promotion, shall not establish any branch, shall not have any supply
         depot or supply the Drager-BIS-Module or [**] to any party other than
         Drager.


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                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                      - 4 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.


         It is understood, however, that in the event that Drager distributes
         [**] and [**] customers using [**] of the number of [**] used by [**].
         Drager shall then grant Aspect a non-exclusive royalty-free right and
         license under its rights to the [**] to [**] Aspect BIS Sensors that
         have been [**] for use with [**] to [**].

2.3      Aspect agrees to provide all reasonable help for Drager with respect to
         the design and/or integration of the Aspect BIS Module Kit into a new
         Drager Workplace.

2.4      Drager agrees [**] the [**] for an [**] equipment.

2.5      Aspect shall obtain any official approvals, permits, licenses and other
         consent required to sell Aspect's BIS Module Kit and Aspect's BIS
         Sensor worldwide, at such time and in such manner as determined by
         Aspect or required by Drager to serve reasonable commercial purposes of
         both companies. Drager shall receive copies of any such documents.

         Drager shall obtain any official approvals, permits, licenses and other
         consent required to sell Drager products worldwide, in such time and in
         such manner as determined by Drager. If necessary, Aspect shall receive
         copies of any such documents belonging to the Drager-BIS-Module and the
         [**]. Aspect will provide any reasonable support required by Drager to
         obtain the necessary approvals for the Drager-BIS-Module and the [**].

2.6      The parties intend to agree on a co-marketing concept for the Products.

3.       PRICES

3.1      The prices for Aspect BIS Module Kits and BIS Sensors shall be as set
         forth in Exhibit B hereto. The price per product is FOB, Boston as per
         Incoterms 1990. All prices for Aspect BIS Module Kits and BIS Sensors
         are exclusive of all taxes, levies and assessments imposed on such
         products purchased hereunder, excluding taxes based on Aspect's
         possession thereof prior to the originally scheduled delivery and taxes
         on Aspect's net income from the transaction. Drager intends to
         introduce the new Drager anesthesia workplace to the market [**].


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                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                      - 5 -


  Confidential Materials omitted and filed separately with the Securities and
                Exchange Commission. Asterisks denote omissions.

3.2      Prices, billing and all payments due hereunder shall be in US$.

3.3      September of each year with effect on 1st January of the following
         year, the prices for Aspect's BIS Module Kit set forth in Exhibit B may
         be adjusted by mutual Agreement. The first adjustment of prices may be
         made prior to October 1, 2002 with effect on January 1, 2003.

         The prices for Aspect's BIS Sensor will be based on the Sensor Price
         Schedule set forth in Exhibit B applied to the prevailing List Price of
         the BIS Sensor in the U.S.

         Any adjustments to BIS Sensor prices may only be made prior to October
         1 of each year for effect on January 1 of the following year. Assuming
         [**] are requested [**] by [**] will be based on the Sensor Price
         Schedule set forth in Exhibit B for the [**] to which will be [**]
         required to [**] the [**] (See also Exhibit A, Section 1.5).

4.       PURCHASE

4.1      All Products shall be ordered in writing, specifying the product type,
         number of units, desired delivery date and means of shipment. Purchase
         orders may be sent by facsimile machine. Such orders shall be
         considered to have been accepted by Aspect only upon Aspect's issuance
         of written acknowledgment confirming its acceptance of the purchase
         order. Aspect's acknowledgment may be sent by facsimile machine and
         shall state delivery date.

4.2      Ownership of, title to, and risk of loss with respect to any product
         sold to Drager hereunder shall pass to Drager upon delivery to carrier
         in Boston packed and ready for shipment to Drager. Aspect shall ship
         products in a manner consistent with Aspect's usual shipping practices.
         Transportation and shipping charges from Boston, including costs
         incurred by Aspect relating to packing, storage, documentation and
         similar items which result from special shipping instructions of
         Drager, and the cost of any insurance which Drager may request in
         connection with the products, shall be added to the price stated on
         invoices and shall be paid by Drager at the time that payment of the
         purchase price for such products is due and payable.


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                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                      - 6 -


  Confidential Materials omitted and filed separately with the Securities and
                Exchange Commission. Asterisks denote omissions.


4.3      Drager shall have the right to handle the purchase of Products via
         another company belonging to the Drager Group. Drager will inform
         Aspect in writing with respect to such decision. Drager will further
         ensure that this company will adhere to the provisions of this
         Agreement.

5.       FORECAST, DELIVERY TIME

5.1      Drager shall provide a non-binding quarterly rolling forecast for a
         minimum of the successive two quarters.

5.2      Aspect shall ship the Products in lots of [**] units.

5.3      Aspect shall ship Aspect BIS Module Kits within (eight) 8 weeks of its
         receipt of purchase orders therefore, assuming the quantity ordered is
         reasonably consistent with the forecast.

5.4      Aspect shall ship [**] within (four) 4 weeks of its receipt of purchase
         orders therefore, assuming the quantity ordered is reasonably
         consistent with the forecast.

5.5      In the event of cancellation of any purchase order, Drager will be
         liable to Aspect for the payment of reasonable cancellation charges.

6.       PAYMENT; INSPECTIONS; RETURNS

6.1      All purchases hereunder shall be paid within thirty (30) days from date
         of invoice to Drager.

6.2      All Products received by Drager shall conform in all material respects
         to the specifications set forth in Exhibit A.

         Receiving inspection by Drager may be performed on a sampling basis
         which shall be in accordance with the Testing Specifications as
         established in Exhibit C. Exhibit C will be negotiated later.


<PAGE>   7
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                      - 7 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

         Acceptance by Drager on a sampling basis shall not prejudice or
         restrict the right of Drager to accumulate and return at Aspect's
         expense for full credit or replacement (freight and insurance prepaid
         to Drager) non-conforming Products discovered during Drager's
         inspection process, which in no event shall extend beyond the warranty
         period provided in Clause 8. Any such return must be made within 30
         days of discovery of any such Products' nonconformance by Drager.

         Aspect must be given the opportunity to inspect and/or correct Products
         for which Drager shall request credit or replacement to enable Aspect
         to determine for itself that said Products do not meet specifications,
         and such credit or replacement shall be made by Aspect only if and when
         it determines that Products do not meet specifications. No Product may
         be returned without Aspect's approval, which, subject to the last
         sentence of the preceding Paragraph under this Clause 6.2, shall not be
         unreasonably withheld.

7.       MODIFICATION OF PRODUCTS

7.1.     Aspect shall inform Drager

         (a)      about planned modifications of Aspect's BIS Module Kit,
                  Aspect's BIS Sensors, [**] and modifications relating to BIS
                  of Aspect's stand alone Monitor,

         (b)      of any modification which will affect the approval of the
                  Products or the Drager Workplace and /or the proper function
                  within the Drager Workplace.

         In case (b), Aspect shall not be allowed to modify Aspect's BIS Module
         Kit, Aspect's BIS Sensor or [**] sold to Drager without Drager's prior
         written consent. Additionally Drager shall have the right to decide if
         Drager wishes to take over the modification. If Drager refuses to take
         over the modification, Aspect shall be obliged to deliver the
         unmodified Aspect BIS Module Kit, Aspect's BIS Sensors and [**] for a
         period of eighteen (18) months beginning with the date Drager announces
         its decision. After this eighteen-months period Aspect can cease to
         deliver the unmodified Aspect BIS Module Kit, Aspect's BIS Sensors or
         [**]. In the event that Aspect believes that a modification or
         improvement relates to patient safety, Drager will accept these
         modifications under the condition that Aspect will agree to repair or
         replace Aspect's BIS Module Kits, Aspect's BIS Sensors or [**]
         previously provided to Drager or Drager customers at no charge.


<PAGE>   8
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                      - 8 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

7.2.     Drager shall promptly inform Aspect of any proposed modification which
         will affect Aspect product approval.

7.3      Aspect agrees in principle to [**] of the [**] and [**] the [**] is
         [**]. Aspect and Drager must agree on a mutually-acceptable time
         schedule and on a mutually-acceptable price for the [**] Aspect shall
         own all right title and interest in any [**] to the Aspect BIS Module
         Kit pursuant to this Section 7.3.

8.       WARRANTY

8.1      Subject to Exhibit E, Aspect hereby warrants to Drager that for a
         period of twelve (12) months after each Product is sold by Drager, or
         an authorized Drager Distributor and delivered to an end user, or
         eighteen (18) months after such Products are received from Aspect by
         Drager, whichever period shall be shorter, that such Products will
         conform in all material respects to the specifications set forth in
         Exhibit A and be free from any defects in workmanship and materials. In
         the event of a breach of the warranty under this Section, Aspect's
         responsibility and Drager's remedy shall first be repair or replacement
         of the Product, at Aspect's option. In the event that, after Aspect has
         attempted to repair or replace the product, the Product does not
         conform to the warranty provided in this Section 8.1, Aspect will
         refund the purchase price for such Product. This paragraph summarizes
         Aspect's responsibility and Drager's sole remedy with respect to the
         warranty set forth in this Section 8.1.

8.2      Notwithstanding the foregoing, Aspect's warranty as set forth above
         does not cover:

         (i)      defects emanating from improper or unauthorized use or
                  maintenance of such products by Drager or any subsequent
                  purchaser thereof;

         (ii)     normal deterioration or normal wear and tear;

         (iii)    disposable items such as the [**] Aspect BIS Sensor after the
                  expiration date marked on the Sensor packaging

         (iv)     catastrophe, fault or negligence of Drager or anyone claiming
                  through or on behalf of Drager; or

         (v)      subject to Exhibit A, causes external to the Products
                  including without limitation power or air conditioning
                  failure.


<PAGE>   9
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                      - 9 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

8.3      THE PROVISIONS OF THE FOREGOING WARRANTIES ARE IN LIEU OF ANY OTHER
         WARRANTY, WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL (INCLUDING ANY
         WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE).


9.       QUALITY ASSURANCE

         Aspect shall adhere to a quality assurance system in accordance with
         the Quality Assurance Agreement as established in Exhibit D.

10.      SERVICE

10.1     Drager assumes full responsibility to render service with respect to
         the maintenance, repair, or replacement of Products, accessory items,
         or parts therefor sold by Drager.

10.2     Aspect agrees to supply Drager, at Drager's expense, with any and all
         special tools and equipment reasonably required for Drager to service,
         maintain or test the Products sold hereunder. Drager agrees to make
         payment for such items to Aspect within thirty (30) days from the date
         of invoice.

10.3     Aspect shall adhere to the Service Agreement as per Exhibit E. Exhibit
         E will be negotiated later.

11.      TRAINING AND DOCUMENTS

         Aspect personnel shall be made available free of charge for a
         reasonable number of training sessions reasonably required by Drager
         with respect to the sales and application know-how, the maintenance,
         repair or replacement of the Products, or parts therefore.

         Aspect will supply Drager free of charge with a reasonable quantity of
         technical, sales and application materials for internal purposes in
         English and German (if available) such as manuals and other technical
         materials relating to the Aspect BIS Module Kits and Aspect's BIS
         Sensors. Aspect will supply Drager at cost price with a reasonable
         quantity of catalogues and literature relating to the Aspect BIS Module
         Kits and Aspect's BIS Sensors.




<PAGE>   10
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 10 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

         Drager agrees to provide, at its own expense, and subject to Aspect's
         prior written approval, translation and printing of technical, sales,
         operation and service materials in the language(s) commonly used in the
         areas where Drager will sell the Products.

         Drager Lubeck will coordinate training and flow of information for all
         Drager participants. Training will be held in English language.

12.      REPLACEMENT PARTS

         Subject to Exhibit E, Aspect agrees to supply Drager with replacement
         parts for the Aspect BIS Module Kits sold hereunder for a period of ten
         (10) years after the date of the last sale of Aspect BIS Module Kits by
         Aspect to Drager hereunder. Prices for the replacement parts will be
         set by Aspect in accordance with Clause 3. Drager shall make payment of
         the replacement parts supplied hereunder within thirty (30) days from
         the date of invoice.

13.      PATENT INDEMNITY

13.1     (a) Except as provided below, Aspect shall defend and indemnify Drager
         from and against any damages, liabilities, costs and expenses
         (including reasonable attorneys' fees) arising out of any claim that
         the Aspect BIS Module, the Aspect BIS Sensor or the [**] infringe a
         valid patent or copyright or misappropriates a trade secret of a third
         party, provided that (i) Drager shall have promptly provided Aspect
         written notice thereof and reasonable cooperation, information, and
         assistance in connection therewith, and (ii) Aspect shall have sole
         control and authority with respect to the defense, settlement, or
         compromise thereof. Should any Product become or, in Aspect's opinion,
         be likely to become the subject of an injunction preventing its use as
         contemplated herein, Aspect may, at its option, (1) procure for Drager
         the right to continue using such product, (2) replace or modify such
         product so that it becomes non-infringing, or, if (1) and (2) are not
         reasonably available to Aspect after consultation in good faith with
         Drager, then (3) terminate Drager's rights to the allegedly infringing
         product and refund to Drager the amount which Drager has paid to Aspect
         for such products which are in the possession of Drager or its
         subdistributors. Drager will immediately inform Aspect as soon as
         Drager becomes aware of any threatened or actual liability claim by a
         third party relating to the Aspect BIS Module, the [**] and the Aspect
         BIS Sensor.


<PAGE>   11
                                                 Drager/Aspect Product Agreement
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                                     - 11 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

         (b) Aspect shall have no liability or obligation to Drager hereunder
         with respect to any patent, copyright or trade secret infringement or
         claim thereof based upon (i) use of the Products by Drager in
         combination with devices or products other than the Drager Workplace,
         (ii) use of the Products in an application or environment for which
         such Products were not designed or contemplated, (iii) modifications,
         alterations or enhancements of the Products not created by or for
         Aspect, or (iv) any claims of infringement of a patent, copyright or
         trade secret in which Drager or any affiliate of Drager has an
         interest. Drager shall indemnify and hold Aspect harmless from all
         costs, damages and expenses (including reasonable attorneys' fees)
         arising from any claim enumerated in clauses (i) through (iv) above,
         provided that (i) Aspect shall have promptly provided Drager written
         notice thereof and reasonable cooperation, information, and assistance
         in connection therewith, and (ii) Drager shall have sole-control and
         authority with respect to the defense, settlement or compromise
         thereof. Aspect will immediately inform Drager as soon as Aspect
         becomes aware of any threatened or actual liability claim by a third
         party relating to Clause (iv) above.

         (c) the foregoing states the entire liability of the Parties with
         respect to infringement of patents, copyrights and trade secrets by the
         Products or any part thereof or by their operation.

13.2     The obligation of the Parties hereto as set forth in this Clause 13
         shall continue notwithstanding the termination of this Agreement.

14.      TRADEMARK

         Any Drager-BIS-Module or [**] sold by Drager under this Agreement shall
         bear the trademark of Drager.

         Drager is required to mark the Drager-BIS-Module and [**] additionally
         to the Drager trademark with the Aspect BIS(TM) trademark as approved
         by Aspect and in accordance with the following provisions:

(a)      Ownership. Drager acknowledges and agrees that Aspect is the sole and
         exclusive owner of all right, title and interest in and to the
         following trademarks (the "Aspect Trademarks"): "Aspect", "BIS", "BIS
         Sensor".

         Drager recognizes the value of the Aspect Trademarks and the good will
         associated with the Aspect Trademarks. Drager agrees that its use of
         the


<PAGE>   12
                                                 Drager/Aspect Product Agreement
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                                     - 12 -


         Aspect Trademarks and any good will arising therefrom shall inure to
         the benefit of Aspect. Nothing contained herein shall create, nor shall
         be construed as an assignment of, any right, title or interest in or to
         the Aspect Trademarks to Drager, other than the grant of a license in
         Section 14(c) below; it being acknowledged and agreed that all other
         right, title and interest in and to the Aspect Trademarks is expressly
         reserved by Aspect. Drager shall keep the Aspect Trademarks free from
         all liens, mortgages or other encumbrances. Drager agrees that it will
         not attack or otherwise challenge the title, validity or any other
         rights of Aspect in or to the Aspect Trademarks.

(b)      Notice. All Products that use the Aspect Trademarks shall be
         accompanied, where reasonable and appropriate, by a proprietary notice
         with respect to Aspect consisting of the following elements:

         1. The statement "[insert trademark(s)] is a proprietary trademark(s)
         of Aspect."

         2. Drager will include the "(TM)" or "(R)" symbol, as instructed by
         Aspect, a reasonable time before the first prominent use of the Aspect
         Trademark in the Products.

         3. Drager shall reproduce copyright and trademark notices of Aspect in
         the relating documents.

(c)      License. Aspect hereby grants to Drager a nonexclusive, worldwide,
         royalty-free license (without the right to sublicense) to use the
         Aspect Trademarks to designate and promote Products. Drager shall have
         no other right to use, display or utilize the Aspect Trademarks for any
         other purpose or in any other manner.

(d)      Quality Standards. Upon reasonable notice and request, Aspect may
         inspect copies of the Products, advertising and promotional materials
         on which the Aspect Trademarks are used so that Aspect may monitor
         compliance with this Agreement. Quality standards are further described
         in Exhibit D to this Agreement.

(e)      Protection and Infringement. Drager agrees to cooperate with and assist
         Aspect in obtaining, maintaining, protecting, enforcing and defending
         Aspect proprietary rights in and to the Aspect Trademarks. In the event
         that Drager learns of any infringement, threatened infringement or
         passing-off of the Aspect Trademarks, or that any third party claims or
         alleges that the Aspect Trademarks infringe the rights of the third
         party or are otherwise liable to


<PAGE>   13
                                                 Drager/Aspect Product Agreement
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                                     - 13 -


         cause deception or confusion to the public, Drager shall be required to
         notify Aspect giving the particulars thereof, and Drager shall provide
         necessary information and assistance to Aspect in the event that Aspect
         decides that proceedings should be commenced.

(f)      Termination. In addition to the termination rights set forth in Section
         21 hereof, in the event that Drager is in material breach of any
         provision of this Section 14, Aspect may, upon 30 days written notice,
         terminate the license granted in Section 14(c) if Drager does not cure
         such breach or default within such 30-day period. The parties recognize
         that curing such breach or default may require development of a new
         version of the Product. If this is the case, then Drager will be deemed
         to have cured such breach or default if, within the 30-day cure period,
         Drager presents to Aspect a plan for revision of the Product that will
         cure such breach or default, such plan is reasonably acceptable to
         Aspect, and such revision is released and distributed within three
         months following written notice of such breach or default.

         In addition to the provisions of Section 21 hereof, upon termination of
         the license granted in Section 14(c), or upon termination of this
         Agreement, for whatever cause except Sections 21.5, 21.6 and 21.7:

         1.       Drager shall immediately cease and desist from any further use
                  of the Aspect Trademarks and any trademarks confusingly
                  similar thereto, either directly or indirectly;

         2.       All rights in the Aspect Trademarks granted to Drager
                  hereunder shall immediately revert to Aspect;

         3.       In the event that this Agreement is terminated for any reason
                  other than a material breach or material default by Drager,
                  Drager shall have a period of 30 days thereafter to dispose of
                  all of the unsold Products bearing the Aspect Trademarks and
                  advertising and promotional materials relating thereto which
                  had been completed by it prior to such termination, provided
                  such Products and materials were in the process of manufacture
                  more than 30 days before such termination.





<PAGE>   14
                                                 Drager/Aspect Product Agreement
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                                     - 14 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

15.      PRODUCT RECALL PROGRAM

         In the event of any recall of the Product by Aspect or required by
         Drager for safety or efficacy reasons resulting from Aspect's failure
         to supply any BIS Module Kits, Aspect BIS Sensors, or [**] that (1)
         conform in all material respects to the specifications set forth in
         Exhibit A or (2) are free from defects in workmanship and materials,
         Aspect agrees to repair or replace all recalled Products previously
         supplied to Drager at no expense to Drager. Aspect also agrees to
         consult with Drager to establish a reasonable process for managing the
         recall. Drager will maintain all necessary sales records to facilitate
         the recall.

16.      PRODUCT LIABILITY

16.1     Aspect will indemnify, protect, and save Drager harmless from all
         claims, demands, suit, or actions for damages to property or person
         which may be sustained by any third party, and which are caused by any
         defect or deficiency in the design or manufacture of any of the
         Products sold to Drager under this Agreement.

         The foregoing indemnity shall survive the expiration or termination of
         this Agreement, but Aspect shall not be responsible for any loss or
         damage caused by acts or omissions of Drager. Aspect shall have no
         liability or responsibility of any kind to Drager under this Clause 16
         for any claims, demands, suits, or actions unless Aspect shall have
         been notified within 30 days time following notification to Drager of
         any such claims, demands, suits, or actions and shall have an adequate
         opportunity to defend. Aspect shall have the sole control and authority
         with respect to the defense, settlement or compromise thereof.

         Should Drager desire to have its own counsel participate in any such
         action or suit, the cost of such counsel shall be borne exclusively by
         Drager. The obligation of the Parties set forth in this Clause 16 shall
         continue notwithstanding the termination of this Agreement.



<PAGE>   15
                                                 Drager/Aspect Product Agreement
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                                     - 15 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

16.2     Drager will indemnify, protect, and save Aspect harmless from all
         claims, demands, suit, or actions for damages to property or person
         which may be sustained by any third party and which are caused by any
         defect or deficiency in the design or manufacture of the Drager
         Workplace or of that portion of the Drager-BIS-Module developed or
         manufactured by Drager, or which relate to the failure of Drager to
         incorporate the Aspect BIS Module Kit within the Drager-BIS-Module in
         accordance with the technical information provided by Aspect, or
         Drager's activities in connection with use or sale of the Products.

         The foregoing indemnity shall survive the expiration or termination of
         this Agreement, but Drager shall not be responsible for any loss or
         damage caused by acts or omissions of Aspect. Drager shall have no
         liability or responsibility of any kind to Aspect under this Clause 16
         for any claims, demands, suits, or actions unless Drager shall have
         been notified within [**] time following notification to Aspect of any
         such claims, demands, suits, or actions and shall have an adequate
         opportunity to defend. Drager shall have sole control and authority
         with respect to the defense, settlement or compromise thereof.

         Should Aspect desire to have its own counsel participate in any such
         action or suit, the cost of such counsel shall be borne exclusively by
         Aspect. The obligation of the Parties set forth in this Clause 16 shall
         continue notwithstanding the termination of this Agreement.

17.      [**] PROJECT

17.1     It is Drager's intention that the Product will become the [**] for
         monitoring the level of hypnosis in Drager anesthesia Workplaces and it
         is [**] of the [**]. However, Drager shall be free to provide
         alternative technology in the event that

         (i)      necessary regulatory approvals for the Products are withdrawn
                  and will not be granted during a [**] period after withdrawn,

         (ii)     approvals have not been granted within a period of [**]
                  following the completion of the Drager-BIS-Module and
                  submission of the necessary requests for approvals to the
                  appropriate regulatory agencies

         (iii)    Aspect is unable to supply Aspect BIS Module Kits in
                  accordance with the specifications and is unable to
                  reinstitute supply within [**] days of written notification

<PAGE>   16
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 16 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

         (iv)     Aspect's market share worldwide for monitoring the effect of
                  anesthesia on the brain with BIS [**].

         (v)      Aspect stops or reduces marketing and product improvement
                  activities materially below the level currently performed.

17.2     Drager may offer in Drager anesthesia workplaces and in other Drager
         products complementary parameters [**] to Aspect's Bispectral Index.
         Any parameter claimed to be a measure of the hypnotic effect of
         anesthetics based on processing of the continuous EEG, is considered to
         be [**] will only be [**] to the BIS.

         Notwithstanding the foregoing, Drager is free to offer EEG parameters
         based on the continuous EEG such as median frequency, spectral edge
         frequency, compressed spectral array (CSA) and/or density spectral
         array (DSA), and may also offer evoked potentials, in addition to the
         BIS.

17.3     In the event that the Aspect's BIS Module Kit sold to Drager contains
         applications unique to Drager Aspect shall for the term of this
         Agreement and for [**] after its termination refrain from selling
         similar products to any third party.

18.      FORCE MAJEURE

         Neither Aspect nor Drager shall be liable for any delay in, or failure
         of, performance hereunder due to any contingency reasonably beyond its
         control, rendering performance commercially unreasonable including, but
         not limited to, an act of God, war (declared or undeclared),
         mobilization, riot, strike, labor dispute, fire, flood, shortages, or
         failure or delays of energy, materials, supplies or equipment,
         unavailability of transportation, goods or services, transportation
         embargoes or delays, or breakdowns in machinery or equipment,
         governmental restrictions or actions but shall not include any royalty
         or other payment imposed or agreed to by Aspect or Drager resulting
         from a third party claim of intellectual property right infringement or
         violation as further described in Clause 13; provided, however, that
         the Party affected shall exert its reasonable best efforts to eliminate
         or cure or overcome any of such causes and to resume performance of its
         covenants.




<PAGE>   17
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 17 -


19.      SECRECY

19.1     If marked as "Confidential Information", Drager and Aspect are each
         obliged to preserve in strict confidence any trade secrets,
         confidential information and technical information of the other Party
         and to refrain from disclosing, during the period of this Agreement and
         any time after expiration of this Agreement, any such information to
         third parties. Notwithstanding the foregoing, information which is
         orally or visually disclosed to the recipient by the disclosing party,
         or is disclosed in writing without an appropriate letter, proprietary
         stamp or legend, shall constitute Confidential Information if the
         disclosing party, within thirty (30) days after such disclosure,
         delivers to the recipient a written document or documents describing
         such Confidential Information and referencing the place and date of
         such oral, visual or written disclosure and the names of the employees
         or officers of the recipient to whom such disclosure was made.

         Both Parties represent and warrant that they have exercised, and will
         continue to exercise the same standard of due care in hiring,
         supervising and selecting those employees to whom they disclose such
         confidential information, so that the confidentiality of all such
         information is protected. No such confidential information disclosed by
         either party to the other in connection with this Agreement shall be
         disclosed to any person or entity other than the recipient's employees
         and contractors directly involved with the recipient's use of such
         information who are bound by written agreement to protect the
         confidentiality of such information, and such information shall be
         otherwise protected by the recipient from disclosure to others with the
         same degree of care accorded to its own proprietary information.

19.2     The Parties' obligation of non-disclosure shall not apply with respect
         to such information, which

         (1)      is already known to the receiving Party before disclosure by
                  the divulging Party, providing that the receiving Party has
                  written records to substantiate its knowledge; or

         (2)      is in the public domain at the time of disclosure to the
                  receiving Party or, after such disclosure, enters into the
                  public domain through no fault of the receiving Party;

         (3)      is independently developed by the receiving Party without
                  reference to or reliance on the Confidential Information; or


<PAGE>   18
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 18 -



         (4)      is lawfully disclosed to the receiving Party by a third party
                  under circumstances permitting its unrestricted disclosure by
                  the receiving party.

         Upon termination of this Agreement, each party shall promptly deliver
         to the other all confidential information of the other party in the
         possession or control of such party and all copies thereof. The
         obligations under this Section 19 shall continue for both parties for a
         period of 3 years after delivery by Aspect to Drager of the last
         Product under this Agreement.

20.      RELATIONSHIP BETWEEN THE PARTIES

         During the term hereof, the relationship of the Parties is that of
         seller (Aspect) and buyer (Drager).

         Nothing herein contained shall be deemed to authorize or empower either
         Party, its affiliates, its agents or employees, to act as agent for the
         other Party or conduct business in the name, or for the account of the
         other Party or any of its affiliates or otherwise bind it or them in
         any manner.

21.      TERM AND TERMINATION

21.1     This Agreement shall come into force when it has been duly signed by
         both Parties and shall remain in force until December 31, 2005, unless
         earlier terminated in accordance with the provisions hereof.

         It shall be automatically renewed thereafter for additional periods of
         one (1) calendar year each unless one Party gives at least twelve (12)
         calendar months prior to the end of the original term hereof and each
         one (1) year period thereafter a written notice to the other Party of
         its intention to terminate. First notice of termination may not be
         given until [**].



<PAGE>   19
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 19 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

21.2     Aspect shall have the right to terminate this Agreement, effective upon
         the delivery of written notice to Drager, in the event Drager fails to
         make any payment when due to Aspect pursuant to this Agreement or any
         invoice for Products. Aspect will [**] to Drager after Drager's receipt
         of Aspect's written demand for payment, provided Aspect has submitted
         proof of delivery in order to rectify any payment problem or
         discrepancy and has stated that the Agreement will be terminated if
         Drager fails to make the due payment within the [**].

21.3     Furthermore, either Party may terminate this Agreement if the other
         Party commits any material breach of its obligations hereunder (other
         than payment defaults addressed in Clauses 21.2 hereof) and such breach
         is not resolved within [**] after written notice thereof is given to
         the Party in breach of this Agreement.

21.4     Should Drager or Aspect at any time during the period of this Agreement
         be adjudged bankrupt or insolvent, or have a Receiver appointed in
         respect of its assets or shall make any arrangement or composition with
         its creditors or shall be wound up, whether voluntarily or
         compulsorily, or make a general assignment for the benefit of
         creditors, then in such event the other Party may, at its option,
         terminate this Agreement effective upon giving notice thereof in
         writing to the other. In the event either Drager or Aspect exercises
         this option, said Party shall incur no liability or obligation with
         respect to said termination.

21.5     In the event of the merger, consolidation or sale of substantially all
         assets of Aspect to a competitor of Drager, Drager may, at its option,
         terminate Section 17 of this Agreement effective upon giving notice
         thereof in writing to Aspect. In the event Drager wishes to exercise
         this option, Drager shall do so within 30 days following written notice
         from Aspect of the merger, consolidation or sale of substantially all
         assets of Aspect, and neither Aspect (or its successors) or Drager
         shall incur liability or obligation with respect to said termination.

         In the event of the merger, consolidation or sale of substantially all
         assets of Drager to a company outside of the Drager-Group, Aspect may,
         at its option, terminate this Agreement effective upon giving notice
         thereof in writing to Drager. In the event Aspect exercises this
         option, Aspect shall do so within 30 days following written notice from
         Drager of the merger, consolidation or sale of substantially all assets
         of Drager, and neither Drager (or its successors) or Aspect shall incur
         liability or obligation with respect to said termination.


<PAGE>   20
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 20 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.


21.6     Subject to the second paragraph of this Section 21.6, in the event of
         termination the Parties agree that Drager shall have the right to
         purchase the Aspect BIS Module Kit and the [**] for [**] following
         termination of the Agreement or Aspect BIS Sensors for [**] following
         termination of the Agreement.

         In the event of termination of the Agreement as a result of a material
         breach of the Agreement by Drager in accordance with Sections 21.2 or
         Section 21.3, Drager shall not be permitted to continue to purchase
         [**] Aspect BIS Sensors beyond [**] termination of the Agreement. If
         Aspect intends to [**] of the [**] the Parties shall [**] in good
         faith.

21.7     In the event of termination, the Parties further agree to finalize
         current sales projects. A complete list of these sales projects has to
         be exchanged by the Parties no later than fourteen (14) days after the
         termination.

21.8     Due to the fact that some Exhibits of this Agreement will be negotiated
         later each Party shall have the right to terminate this Agreement if
         the parties cannot reasonably agree on the content of one of these
         Exhibits.

22.      MISCELLANEOUS

22.1     This Agreement shall not be assignable either in whole or in part
         without the prior written consent of the other Party except, subject to
         Section 21.5, to a party that acquires all or substantially all of
         either Parties' business by merger, sale of assets, or otherwise.

22.2     Subject to Clause 21.1 hereof, this Agreement shall inure to the
         benefit of and be binding upon the Parties hereto.

22.3     The headings used herein are for ease of reference only and are not to
         be used in interpretation or construction of this Agreement.

22.4     The provisions of this Agreement and its Exhibits shall not be
         extended, varied, changed, modified or supplemented other than by
         agreement in writing signed by the Parties hereto.

22.5     In the event of any inconsistency or conflict between the provisions of
         this Agreement and any Purchase Order or other document, the provisions
         of this Agreement shall prevail.


<PAGE>   21
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 21 -



22.6     All notices or other communications which shall or may be given
         pursuant to this Agreement shall be in writing in the English language
         and shall be delivered by personal delivery, certified mail, or telefax
         at the address set forth below, or at such other address as such party
         may hereafter designate in writing as the appropriate address for the
         receipt of such notice.

           To Aspect at:

              Aspect Medical Systems, Inc.
              2 Vision Drive
              Natick
              MA 01760-2059
              USA
              Tel.: 508-647-2072
              Fax:   508-647-2059
              Attention: J.Breckenridge Eagle

           To Drager at:

              Drager Medizintechnik GmbH
              Moislinger Allee 53 - 55
              D-23558 Lubeck
              Federal Republic of Germany
              Tel.:  451-882-2295
              Fax:   451-882-2793
              Attention: Business Unit Anaesthesia, Swen Grunitz-Post

         All notices shall be deemed served on the day on which personally
         served, or of by certified mail, or telefax on the date of actual
         receipt.

21.7     The waiver by either Party hereto of any default hereunder or of any
         breach of any covenant, agreement or condition contained herein shall
         not be construed to constitute a waiver of any other default or breach
         hereof whether similar or otherwise.

22.8     If any provision of this Agreement should be held unenforceable, or
         illegal with respect to any jurisdiction, it (i) shall be deemed
         severable from the other provisions which shall remain valid and
         enforceable; and (ii) shall remain in effect in other jurisdiction
         where such provision is otherwise enforceable and legal.



<PAGE>   22
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 22 -


         This Agreement may be executed simultaneously in multiple counterparts,
         each of which shall be deemed an original and all of which together
         shall constitute one and the same agreement.

22.10    Neither party shall have the right to sublicense any of the rights or
         licenses granted under this agreement outside the company group without
         the other's prior written consent.

21.11    Compliance with Laws. Drager shall comply with all laws, legislation,
         rules, regulations, governmental requirements and industry standards
         with respect to the Products, and the performance by Drager of its
         obligations hereunder, existing in any jurisdiction into which Drager
         directly or indirectly distributes the Products. Aspect shall inform
         Drager if export of Aspect's BIS Module Kit or Aspect's Sensors are
         restricted to any country or require certain permission in any country.

21.12    IN THE EVENT THAT U.S. LAW IS APPLIED TO THIS AGREEMENT, ASPECT OR
         DRAGER SHALL NOT BE LIABLE FOR ANY LOSS OF DATA, LOSS OF PROFITS OR
         LOSS OF USE OF THE PRODUCTS OR FOR ANY INDIRECT DAMAGES OF ANY KIND
         (WHETHER SPECIAL, INCIDENTAL, CONSEQUENTIAL OR OTHER INDIRECT DAMAGES)
         IN CONNECTION WITH THE USE OR PERFORMANCE OF THE PRODUCTS.

23.      APPLICABLE LAW

         This Agreement shall be governed, construed and interpreted in
         accordance with the laws of Switzerland, without regard to its conflict
         of laws principles.

         The United Nations Convention on contracts for the International Sale
         of Goods shall not apply.

24.      DISPUTE SETTLEMENT, PLACE OF JURISDICTION

24.1     The Parties shall try to settle any dispute arising in connection with
         this present Agreement amicably. In case of a local sales conflict a
         task force of Drager and Aspect consisting of the persons named under
         Clause 22.6 will take care of such dispute settlement.

24.2     In the event disputes cannot be settled amicably according to Clause
         24.1, in connection with this present Agreement shall be exclusively
         and finally settled by the courts of Zurich.

Natick, ......April 29, 1999.....       Lubeck, .......May 5, 1999..............

J. Breckenridge Eagle                   [Illegible]
 .................................       ........................................
Aspect Medical Systems, Inc.            Drager Medizintechnik GmbH



<PAGE>   23
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 23 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

EXHIBIT A


of the               Drager/Aspect Product Agreement
between              Aspect Medical Systems, Inc.
and                  Drager Medizintechnik GmbH


Products

1.1      The Drager-BIS-Module will incorporate Aspect's BIS Module Kit.

         Aspect's BIS 'Module Kit' is designed specifically for OEM applications
         and allows the integration of Aspect's BIS monitoring technology into
         OEM equipment. The BIS Engine will interface to the patient via the
         Aspect BIS sensor and to the OEM equipment utilizing a serial (RS-232)
         3-wire interface and the necessary power connections.

         The BIS Module Kit consists of a Digital Signal Converter (DSC-2) that
         is placed in proximity to the patient and a small circuit board that
         resides in the OEM equipment. The DSC-2 is a small (palm sized)
         front-end to the BIS Engine circuit board that provides the patient
         interface and performs the high performance analog to digital
         conversion of the EEG signals. The EEG signals are transmitted in
         digital format from the DSC-2 to the BIS engine circuit board via a 12
         foot cable that is hard wired connected at the DSC-2.

         The BIS Engine circuit board measures 3 x 4 inches. This board performs
         digital signal processing on the digitized EEG signal and outputs the
         Bispectral Index to the OEM system via the RS-232 serial connection.
         The board is constructed using double sided surface mount techniques.
         The connections to the BIS Engine circuit board are a serial interface
         (RS-232), power, and DSC connections.



<PAGE>   24

                                                 Drager/Aspect Product Agreement
                                                                        20.04.99

     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.



                                     - 24 -


       Detailed Technical Specifications:

       Digital Output:             [**]

       Main Parameters:            [**]

       Electrical Safety:          [**]

       Power:                      [**]

       Artifact Rejection:         [**]

       Bispectral Index:           [**]


       Digital Signal Converter (DSC-2)

       Description:                [**] to the [**]

       Weight:                     [**]

       Dimensions:                 [**]

       Cable Length:               [**]


       BIS Engine PCB

       Physical:                   [**]

       Processing Power:           [**]


       Software Upgrades
       [**] software is stored in [**]. Software upgrades can be accomplished
       [**] via the [**].


       Serial Identifier
       Each [**] serial identifier. This allows for [**].




<PAGE>   25
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 25 -



     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.

                  [Graphic of Aspect BIS Module Kit and Sensor]

1.2      In addition to the main parameters indicated in Exhibit A, Section 1.1,
         the Aspect BIS Module Kit shall also provide the [**].

         When the Drager-BIS-Module is in use in a Drager Workplace System,
         there will be a possibility to display each of the following [**] as
         well as the [**] in the [**] when used for [**] and in [**].

1.3      Aspect shall ensure that all BIS enhancements that Aspect develops for
         Aspect's stand alone BIS monitor will be available in the BIS Module
         Kit sold to Drager as appropriate and as soon as reasonably possible.

         Drager will agree to distribute a modified BIS Sensor in the event
         Aspect determines that an enhancement to the BIS Module Kit requires
         the use of a modified Sensor. All conditions, prices and so on won't be
         changed for the new sensors. If this occurs, and if [**] in accordance
         with Section 1.5 of Exhibit A, [**] to provide a [**] of the [**] for
         the [**] use of [**]. Possible additional costs will be incorporated in
         the transfer price for the [**] and reasonable volumes will be
         required.

         In the event that Aspect develops a different product involving a
         different type of index, patient sensor, or application, Aspect and
         Drager will develop a mutually-satisfactory new, or amended, agreement.

1.4      For integration into a Drager Workplace, Drager will design an Drager
         Workplace specific Drager-BIS-Module. Aspect will grant all reasonable
         help to Drager designing the Drager-BIS-Module.

1.5      On the [**]. The possibility to use [**] the original Aspect BIS
         monitor will be negotiated later. Possible additional costs [**] will
         be incorporated in the transfer price and [**] will be required.

1.6      Both Parties agree to work out a common technical requirement
         specification for the Products. The latest version of this technical
         requirement specification signed by both Parties will be the
         specification of the Product to be manufactured by Aspect for Drager.

Natick, .....4/29/99.............       Lubeck, .........May 5, 1999 ...........

J. Breckenridge Eagle                   [illegible]
 .................................       ........................................
Aspect Medical Systems, Inc.            Drager Medizintechnik GmbH


<PAGE>   26
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 26 -



     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.


         EXHIBIT B


         of the                    Drager/Aspect Product Agreement
         between                   Aspect Medical Systems, Inc.
         and                       Drager Medizintechnik GmbH


         PRICES AND DISCOUNTS

         The price for one Aspect BIS Module Kit is US$[**].

         The components consists of a [**] and [**] and a [**] and [**].

         Drager shall have the right to manufacture on a royalty free basis the
         circuit board based on design specifications provided by Aspect. In
         this case the price for the remaining components is US$[**] for one
         Aspect BIS Module Kit. The Parties will agree in the future on the
         terms of a manufacturing license.

         The price of the Aspect BIS Module Kit always includes 5 Sensors.
         Drager agrees to supply these Sensors together with each
         Drager-BIS-Module to its customers.

         The Parties agree that Aspect will grant to Drager an additional
         discount on the price of the Aspect BIS Module Kit depending on a
         certain yearly quantity : Aspect will grant an additional discount of
         [**] for a yearly quantity of more than [**] Aspect BIS Module Kits.

         Aspect [**] the [**] subsequent to the date of this agreement, for
         products sold by Aspect [**] to other customers of Aspect [**]. Aspect
         will provide Drager with a [**] to [**] that [**] by other Aspect
         customers.

         The price to Drager for the Aspect-BIS-Sensor will be as follows:

         The transfer price to Drager for the Aspect BIS Sensor will vary
         between[**] of the List Price of the Aspect BIS Sensor in the United
         States. This is equivalent to a discount off of Aspect's List price in
         the United States for the BIS Sensor between [**].


<PAGE>   27
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 27 -


     Confidential Materials omitted and filed separately with the Securities
              and Exchange Commission. Asterisks denote omissions.


         As of January 1, 1999, the List Price for Aspect's BIS Sensor is
         US$15.00 The actual amount of the discount off the U.S. List Price will
         depend upon the volume of Aspect BIS Sensors shipped by Drager for use
         with Drager-BIS-Modules. Prior to the shipment by Drager of the first
         [**]Drager-BIS-Modules, the discount available to Drager for purchase
         of the Aspect BIS Sensors will be set at [**] of Aspect's List Price
         for the BIS Sensor in the United States. Following the shipment of the
         first [**] Drager-BIS-Modules, the discount available to Drager will
         depend upon the volume of Aspect BIS Sensors shipped each quarter
         divided by the number of documented Drager-BIS-Modules installed minus
         the first [**] Drager-BIS-Modules installed. Using this formula, the
         Aspect BIS Sensor price schedule is as follows:

Sensor Shipments per module per quarter-Note 1        Discount off US List price
----------------------------------------------        --------------------------

  up [**]                                             [**]
   [**]                                               [**]
   [**]                                               [**]
   [**]                                               [**]
   [**]                                               [**]
   [**]                                               [**]
or more [**]                                          [**]

Note 1: Sensor consumption rate calculated based on total Aspect BIS Sensors
shipped during the quarter divided by the average Drager-BIS Module installed
base during the quarter minus [**].

In the event that Drager requests that Aspect develop the Drager-BIS-Sensor,
Aspect will sell Drager-BIS-Sensors to Drager in accordance with the same
discount schedule as above, with possible additional costs as noted in Section
1.5 of Exhibit A.

According to Clause 2.1 of the Agreement Drager shall not distribute Sensors in
the USA. Therefore, Aspect will pay a commission to Drager of [**] of the
amounts paid by the customer for each Sensor shipped for use with a
Drager-BIS-Module in the USA.



 Natick, .......4/29/99 ............           Lubeck, ......May 5, 1999  ......

 J. Breckenridge Eagle                         [illegible]
 ...................................           .................................
 Aspect Medical Systems, Inc.                  Drager Medizintechnik GmbH

<PAGE>   28
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 28 -




EXHIBIT C


of the                    Drager/Aspect Product Agreement
between                   Aspect Medical Systems, Inc.
and                       Drager Medizintechnik GmbH



TESTING SPECIFICATIONS FOR THE PRODUCTS



(to be negotiated later)




Natick, .......4/29/99 ................   Lubeck, ......May 5, 1999  .......

J. Breckenridge Eagle                     [illegible]
 .......................................   ..................................
Aspect Medical Systems, Inc.              Drager Medizintechnik GmbH




<PAGE>   29
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 29 -



EXHIBIT D


of the                    Drager/Aspect Product Agreement
between                   Aspect Medical Systems, Inc.
and                       Drager Medizintechnik GmbH




QUALITY ASSURANCE AGREEMENT





(to be negotiated later)








Natick, .......4/29/99 .................         Lubeck, ......May 5, 1999  ....

J. Breckenridge Eagle                            [illegible]
 ........................................         ...............................
Aspect Medical Systems, Inc.                     Drager Medizintechnik GmbH

<PAGE>   30
                                                 Drager/Aspect Product Agreement
                                                                        20.04.99
                                     - 30 -

EXHIBIT E


of the        Drager/Aspect Product Agreement
between       Aspect Medical Systems, Inc.
and           Drager Medizintechnik GmbH


SERVICE AGREEMENT





(to be negotiated later)













Natick, .......4/29/99 .................         Lubeck, ......May 5, 1999  ....

J. Breckenridge Eagle                            [illegible]
 ........................................         ...............................
Aspect Medical Systems, Inc.                     Drager Medizintechnik GmbH