<PAGE>
                                                                     Exhibit 4.2


                               WARRANT AGREEMENT

                                 By and Between

                               MICRUS CORPORATION

                                      and

                          ROBERTS MITANI CAPITAL, LLC

                         Dated as of December 11, 2000




<PAGE>
                               WARRANT AGREEMENT

          WARRANT AGREEMENT dated as of December 11, 2000 by and between MICRUS
CORPORATION, a Delaware corporation (the "Company"), and ROBERTS MITANI
CAPITAL, LLC (the "Agent").

          The Company proposes to issue to the Agent a warrant as hereinafter
described (the "Agent Warrant") to purchase up to an aggregate 377,142 shares,
subject to adjustment as provided in Section 8 hereof (such shares, as adjusted,
being hereinafter referred to as the "Shares") of the Company's Class A Common
Stock, par value $0.001 per share (the "Common Stock"). All capitalized terms
used herein and not otherwise defined herein shall have the same meanings as in
that certain Engagement Agreement, dated March 24, 2000, as amended April 30,
2000, by and between the Company and the Agent (the "Engagement Agreement").

          NOW, THEREFORE, in consideration of the premises and the mutual
agreements herein set forth and for other good and valuable consideration, the
parties hereto agree as follows;

          1.   Issuance of Warrants: Form of Warrant.  The Company will issue,
sell and deliver the Agent Warrant to the Agent or its bona fide officers
and/or directors. The form of the Agent Warrant and the form of election to
purchase Shares to be attached thereto shall be substantially as set forth on
Exhibit A attached hereto. The Agent Warrant shall be executed on behalf of the
Company by the manual or facsimile signature of the present or any future
President and Chief Operating Officer or any Vice President of the Company, and
attested by the manual or facsimile signature of the present or any future
Secretary or Assistant Secretary of the Company.

          2.   Agent Warrant Registration.  The Agent Warrant shall be numbered
and shall be registered in a register to be maintained by the Company (the
"Agent Warrant Register"). The Company shall be entitled to treat the registered
holder of the Agent Warrant on the Agent Warrant Register (the "Holder") as the
owner in fact thereof for all purposes and shall not be bound to recognize any
equitable or other claim to or interest in such Agent Warrant on the part of any
other person, and shall not be liable for any registration of transfer of the
Agent Warrant which are registered or are to be registered in the name of a
fiduciary or the nominee of a fiduciary unless made with the actual knowledge
that a fiduciary or nominee is committing a breach of trust in requesting such
registration of transfer, or with such knowledge of such facts that its
participation therein amounts to be bad faith. The Agent Warrant shall be
registered initially in the name of Roberts Mitani Capital, LLC in such
denomination as the Agent may request in writing to the Company; provided,
however, that the Agent may designate that all or a portion of the Agent Warrant
be issued in varying amounts in separate Agent Warrants directly to its bona
fide officers, directors, employees and/or consultants and not to the Agent.

          3.   Transfer of Warrants.  Subject to compliance with applicable
federal and state securities laws, the Agent Warrant and all rights hereunder
are transferable in whole or in part by the Holder to any person or entity upon
written notice to the Company; provided, however, that to the extent the
transferee is not a party to the Company's Amended and Restated Stockholders'
Agreement dated August 28, 2000, as amended from time to time (the
"Stockholders' Agreement"), such transfer shall be further subject to such
transferee agreeing in writing that upon exercise of this Warrant such
transferee and the Warrant Shares issued upon exercise of this Warrant will be
subject to the Stockholders' Agreement. In all cases of transfer


                                       2
<PAGE>
by an attorney, the original power of attorney, duly approved, or an official
copy thereof, duly certified, shall be deposited with the Company. In case of
transfer by executors, administrators, guardians or other legal representatives,
duly authenticated evidence of their authority shall be produced, and may be
required to be deposited with the Company in its discretion. Upon any
registration of transfer, the Company shall deliver a new Agent Warrant or Agent
Warrants to the persons entitled thereto. The Agent Warrants may be exchanged at
the option of the Holder thereof for another Agent Warrant, or other Agent
Warrants, of different denominations, of like tenor and representing in the
aggregate the right to purchase a like number of shares of Common Stock upon
surrender to the Company or its duly authorized agent.

          4.        Term of Warrants: Exercise of Warrants

                    (a)       The Agent Warrant entitles the Holder thereof to
purchase the Shares at a purchase price of $3.84 per Share (the "Exercise
Price") at any time from the date of this Warrant Agreement until 5:00 p.m.,
Eastern Standard Time, on, December 11, 2005 (the "Warrant Expiration Date").
Prior to the Warrant Expiration Date, the Company will not take any action which
would terminate the Agent Warrant. The Exercise Price and the Shares issuable
upon exercise of the Agent Warrant are subject to adjustment upon the occurrence
of certain events, pursuant to the provisions of Section 8 of this Agreement.
Subject to the provisions of this Agreement, each Holder shall have the right,
which may be exercised as set forth below and in such Agent Warrant, to purchase
from the Company (and the Company shall issue and sell to such Holder) the
number of fully paid and nonassessable shares of Common Stock specified in such
Agent Warrant as follows:

     (i)                 Cash Exercise. The exercise may be effected by the
                         surrender of the Agent Warrant, together with a duly
                         executed copy of the form of Notice of Election
                         attached thereto, to the Secretary of the Company at
                         its principal offices; and the payment to the Company
                         of an amount equal to the aggregate Exercise Price for
                         the number of shares of Common Stock being purchased;
                         or

     (ii)                Net Exercise. In lieu of exercising this Warrant
                         pursuant to (i) above, the Holder may elect to receive,
                         without the payment by the Holder of any additional
                         consideration, shares of Common Stock equal to the
                         value of the Agent Warrant (or the portion thereof
                         being canceled) by surrender of the Agent Warrant at
                         the principal office of the Company together with
                         notice of such election, in which event the Company
                         shall issue to the holder hereof a number of shares of
                         Common Stock computed using the following formula:

                         X =       Y(A-B)
                                   ------
                                     A

               Where:

               X = The number of shares of Common Stock to be issued to the
               Holder pursuant to this net exercise;

               Y = The number of shares of Common Stock in respect of which the
               net issue election is made;



                                       3
<PAGE>
     A = The Fair Market Value of one share of the Common Stock at the time the
     net issue election is made;

     B = The Exercise Price (as adjusted to the date of the net issuance).

For purposes of this Section 4, the "Fair Market Value" of one share of Common
Stock as of a particular date shall be as determined pursuant to Section 4(b)
hereof; provided, that, if the Agent Warrant is being exercised upon the closing
of the Company's initial public offering, the value will be the initial "Price
to Public" of one share of Common Stock specified in the final prospectus with
respect to such offering.

     (b)  For the purpose of any computation under this Agreement, the Fair
Market Value per share of Common Stock at any date shall be:

     (i)  if the Common Stock is publicly traded, the average of the daily
closing prices for fifteen (15) consecutive trading days commencing twenty (20)
trading days before the date of such computation. The closing price for each
day shall be the last reported sale price regular way or, in case no such
reported sale takes place on such day, the average of the closing bid and asked
prices regular way for such day, in either case on the principal national
securities exchange on which the shares are listed or admitted to trading, or
if they are not listed or admitted to trading on any national securities
exchange, but are traded in the over-the-counter market, the closing sale price
of the Common Stock or, in case no sale is publicly reported, the average of
the representative closing bid and asked quotations for the Common Stock on the
National Association of Securities Dealers Automated Quotations ("NASDAQ")
system or any comparable system, or if the Common Stock is not listed on the
NASDAQ system or a comparable system, the closing sale price of the Common
Stock or, in case no sale is publicly reported, the average of the closing bid
and asked prices as furnished by two members of the NASD selected from time to
time by the Company for that purpose; and

     (ii) if the Common Stock is not publicly traded, the price per share of
the Company's most recent offering of newly issued stock, whether common or
preferred.

     (c)  Upon each surrender of the Agent Warrant in accordance with Section
4(a)(i) or (ii) hereof, the Company shall issue and cause to be delivered with
all reasonable dispatch to or upon the written order of the Holder of such
Agent Warrants and in such name or names as such Holder may designate (so long
as surrender or transfer would not violate the Act or any applicable state
securities laws), a certificate or certificates for the number of full Shares
so purchased upon the exercise of such Agent Warrant, together with cash, as
provided in Section 9 of this Agreement, in respect of any fractional Shares
otherwise issuable upon such surrender. Such certificate or certificates shall
be deemed to have been issued and any person so designated to be named therein
shall be deemed to have become a holder of record of such Shares as of the date
of the surrender of the Agent Warrant as aforesaid (and payment of the Exercise
Price with respect to Section 4(a)(i) hereof). The rights of purchase
represented by the Agent Warrant shall be exercisable, at the election of the
Holder thereof, either in full or from time to time in part and, in the event
that any Agent Warrant is exercised in respect of less than all of the Shares
issuable upon such exercise at any time prior to the Warrant Expiration Date, a
new Agent Warrant or Agent Warrants will be issued for the remaining number of
Shares specified in the Agent Warrant so surrendered.

     (d)  The Holder agrees that upon exercise of the Agent Warrant such Holder
and the Shares issued upon exercise of the Agent Warrant will be subject to the
Stockholders' Agreement, including all rights and obligations therein, and will
enter into such agreements and instruments reasonably requested by


                                       4
<PAGE>
the Company to be bound by such Stockholders' Agreement.

     5.   Payment of Taxes. The Company will pay all documentary stamp taxes, if
any, attributable to the issuance of Shares upon the exercise of the Agent
Warrants.

     6.   Mutilated or Missing Warrants. In case any of the Agent Warrants shall
be mutilated, lost, stolen or destroyed, the Company may, in its discretion,
issue and deliver in exchange and substitution for and upon cancellation of the
mutilated, lost, stolen or destroyed Agent Warrant, a new Agent Warrant of like
tenor and representing an equivalent right or interest, but only upon receipt of
evidence or an affidavit of Holder reasonably satisfactory to the Company of
such mutilation, loss, theft or destruction of such Agent Warrant. An applicant
for such substitute Agent Warrants shall also comply with such other reasonable
regulations and pay such other reasonable charges as the Company may prescribe.

     7.   Reservation of Shares, etc. There have been reserved, and the Company
shall at all times keep reserved, out of the authorized and unissued Common
Stock, a number of shares of Common Stock sufficient to provide for the exercise
of the rights of purchase represented by the outstanding Agent Warrants. Any
transfer agent for the Common Stock (the "Transfer Agent"), and every subsequent
transfer agent, if any, for the Company's securities issuable upon the exercise
of the Agent Warrants will be irrevocably authorized and directed at all times
until the Warrant Expiration Date to reserve such number of authorized and
unissued shares as shall be required for such purpose. The Company will keep a
copy of this Agreement on file with the Transfer Agent and with every subsequent
transfer agent for any shares of the Company's securities issuable upon the
exercise of the Agent Warrants. The Company will supply the Transfer Agent or
any subsequent transfer agent with duly executed certificates for such purpose
and will itself provide or otherwise make available any cash which may be
distributable as provided in Section 9 of this Agreement. All Agent Warrants
surrendered in the exercise of the rights thereby evidenced shall be canceled,
and such canceled Agent Warrants shall constitute sufficient evidence of the
number of Shares that have been issued upon the exercise of such Agent Warrants.
No shares of Common Stock shall be subject to reservation in respect of
unexercised Agent Warrants subsequent to the Warrant Expiration Date.

     8.   Adjustments of Exercise Price and Number of Shares. The Exercise Price
and the number and kind of securities issuable upon exercise of each Agent
Warrant shall be subject to adjustment from time to time upon the happening of
certain events, as follows:

          (a)  Subdivisions, Combinations and Other Issuances. If the Company
shall at any time prior to the expiration of this Warrant subdivide its Common
Stock, by split-up or otherwise, or combine its Common Stock, or issue
additional shares of its Preferred Stock or Common Stock (or rights, options or
warrants or convertible or exchangeable securities containing the right to
subscribe for or purchase shares of Common Stock) as a dividend with respect to
any shares of its Common Stock, the number of Warrant Shares issuable on the
exercise of this Warrant shall forthwith be proportionately increased in the
case of a subdivision or stock dividend, or proportionately decreased in the
case of a combination. Appropriate adjustments shall also be made to the
purchase price payable per share, but the aggregate purchase price payable for
the total number of Warrant Shares purchasable under this Warrant (as adjusted)
shall remain the same. Any adjustment under this Section 8(a) shall become
effective at the close of business on the date the subdivision or combination
becomes effective, or as of the record date of such dividend, or in the event
that no record date is fixed, upon the making of such dividend.

          (b)  Reclassification, Reorganization and Consolidation. In case of
any reclassification, capital reorganization, or change in the capital stock of
the Company (other than as a result of a


                                       5
<PAGE>
subdivision, combination, or stock dividend provided for in Section 8(a) above)
then, as a condition of such reclassification, reorganization, or change, lawful
provision shall be made, and duly executed documents evidencing the same from
the Company or its successor shall be delivered to the Holder, so that the
Holder shall have the right at any time prior to the expiration of this Warrant
to purchase, at a total price equal to that payable upon the exercise of this
Warrant, the kind and amount of shares of stock and other securities and
property receivable in connection with such reclassification, reorganization, or
change by a holder of the same number of shares of Common Stock as were
purchasable by the Holder immediately prior to such reclassification,
reorganization, or change. Such reclassification, reorganization and
consolidation may include without limitation a transfer of Company's assets to
an affiliate company to be formed under the laws of Switzerland or similar
entity. In any such case, appropriate provisions shall be made with respect to
the rights and interest of the Holder so that the provisions hereof shall
thereafter be applicable with respect to any shares of stock or other securities
and property deliverable upon exercise hereof, and appropriate adjustments shall
be made to the purchase price per share payable hereunder, provided the
aggregate purchase price shall remain the same.

      (c) Whenever the number of Shares purchasable upon the exercise of each
Agent Warrant is adjusted, as herein provided, the Exercise Price shall be
adjusted by multiplying the Exercise Price in effect immediately prior to such
adjustment by a fraction, of which the numerator shall be the number of Shares
purchasable upon the exercise of each Agent Warrant immediately prior to such
adjustment, and of which the denominator shall be the number of Shares so
purchasable immediately thereafter.

      (d) Upon the expiration of any rights, options, warrants, conversion
rights or exchange privileges, if any thereof shall not have been exercised, the
Exercise Price and the number of shares of Common Stock purchasable upon the
exercise of each Agent Warrant shall, upon such expiration, be readjusted and
shall thereafter be such as it would have been had it originally been adjusted
(or had the original adjustment not been required, as the case may be) as if (i)
the only shares of Common Stock so issued were the Common Stock, if any,
actually issued or sold upon the exercise of such rights, options, warrants or
conversion rights or exchange privileges and (ii) such Common Stock, if any,
were issued or sold for the consideration actually received by the Company upon
such exercise plus the aggregate consideration, if any, actually received by the
Company for the issuance, sale or grant of all of such rights, options, warrants
or conversion rights or exchange privileges whether or not exercised; provided,
however, that no such readjustment shall have the effect of increasing the
Exercise Price by an amount in excess of the amount of the adjustment initially
made in respect to the issuance, sale or grant of such rights, options,
warrants, conversion rights or exchange privileges.

      (e) The Company may, at its option, at any time during the term of the
Agent Warrants, reduce the then current Exercise Price to any amount deemed
appropriate by the Board of Directors of the Company, for any length of time.

      (f) Whenever the number of Shares issuable upon the exercise of each Agent
Warrant or the Exercise Price of such Shares if adjusted, as herein provided,
the Company shall promptly mail by first class mail postage prepaid, to each
Holder notice of such adjustment or adjustments at such Holder's address
appearing on the Agent Warrant Register. The Chief Financial Officer of the
Company shall make any computation required by this Section 8 and shall execute
a certificate (the "CFO Certificate") setting forth the number of Shares
issuable upon the exercise of each Agent Warrant and the Exercise Price of such
Shares after such adjustment, setting forth a brief statement of the facts
requiring such adjustment and setting forth the computation by which such
adjustment was made. Each Holder shall have the right to inspect the CFO
Certificate during reasonable business hours. In the event that a Holder shall
dispute the determination set forth in the CFO Certificate, the Company shall
retain, at its expense, a firm of independent public accountants (who


                                       6
<PAGE>
may be regular accountants employed by the Company) to make the required
computation and to prepare a certificate which shall set forth the information
required in the CFO Certificate. Such certificate shall be conclusive on the
correctness of such adjustment and each Holder shall have the right to inspect
such certificate during reasonable business hours.

          (g)  Except as provided in this Section 8, no adjustment in respect of
any dividends shall be made during the term of an Agent Warrant or upon the
exercise of an Agent Warrant.

          (h)  In case of any consolidation of the Company with or merger of,
the Company with or into another corporation or in case of any sale or
conveyance to another corporation of the property of the Company as an entirety
or substantially as an entirety, the Company or such successor or purchasing
corporation (or an affiliate of such successor or purchasing corporation), as
the case may be, agrees that each Holder shall have the right thereafter upon
payment of the Exercise Price in effect immediately prior to such action to
purchase upon exercise of each Agent Warrant the kind and amount of shares and
other securities and property (including cash) which he would have owned or have
been entitled to receive after the happening of such consolidation, merger, sale
or conveyance had such Agent Warrant been exercised immediately prior to such
action. The provisions of this paragraph (k) shall similarly apply to successive
consolidations, mergers, sales or conveyances.

          (i)  Notwithstanding any adjustment in the Exercise Price or the
number or kind of shares purchasable upon the exercise of the Agent Warrants
pursuant to this Agreement, certificates for the Agent Warrants issued prior or
subsequent to such adjustment may continue to express the same price and number
and kind of Shares as are initially issuable pursuant to this Agreement.

          (j)  For the purpose of this Section 8, the term "shares of Common
Stock" shall mean (i) the class of stock designated as the Common Stock of the
Company at the date of this Agreement or (ii) any other class of stock resulting
from successive changes or reclassifications of such shares consisting solely of
changes in par value, or from no par value to par value, or from par value to no
par value. In the event that at any time, as a result of an adjustment made
pursuant to paragraphs (a) or (b) above, the Holders shall become entitled to
purchase any shares of capital stock of the Company other than Common Stock,
thereafter the number of such other shares so purchasable upon exercise of each
Agent Warrant and the Exercise Price of such Shares shall be subject to
adjustment from time to time in a manner and on terms as nearly equivalent as
practicable to the provisions with respect to the Shares contained in paragraphs
(a) or (b) above, and the provisions of Sections 4, 5, 7 and 10, with respect to
the Shares, shall apply on like terms to any such other shares.

     9. Fractional Interests. The Company shall not be required to issue
fractions of Shares on the exercise of the Agent Warrants. If more than one
Agent Warrant shall be presented for exercise in full at the same time by the
same Holder, the number of Shares which shall be issuable upon the exercise
thereof shall be computed on the basis of the aggregate number of Shares
issuable on exercise of the Agent Warrants so presented. If any fraction of a
Share would, except for the provisions of this Section 9, be issuable on the
exercise of any Agent Warrant (or specified portions thereof), the Company shall
purchase such fraction for an amount in cash equal to the same fraction of the
Current Market Price per share of Common Stock on the date of exercise.

     10. Registration Rights.

     (a) The Company shall provide to the Agent or any subsequent Holders of the
Shares those registration rights provided for Holders of shares of the Company's
stock as provided in Section 4 of the


                                       7
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Stockholders' Agreement, including participatory registration rights for a
Designated Offering and Piggyback Registration rights, as defined in the
Stockholders' Agreement. These registration rights are provided pursuant to this
Warrant Agreement and shall remain in effect for the term of this Warrant
Agreement, notwithstanding any termination or amendment of the Stockholders'
Agreement. The registration rights granted pursuant to this Section 10(a) will
remain, however, governed by the definitions and conditions of the Stockholders'
Agreement, including the notice, exercise and participation time periods
thereof, notwithstanding any termination or amendment of the Stockholders'
Agreement.

            (b) For purposes of this Section 10, the term "Holder" shall include
holders of Shares. Nothing in this Section 10, however, shall be deemed to
require the Company to register the Agent Warrant, it being understood that the
registration rights granted hereby relate only to the Shares issuable or issued
upon exercise of the Agent Warrants and any securities issued in substitution or
exchange therefor.

      11. Notices to Holders.

            (a) Nothing contained in this Agreement or in the Agent Warrant
shall be construed as conferring upon the Holders thereof the right to vote or
to receive dividends or to consent or to receive notice as shareholders in
respect of the meetings of shareholders or the election of directors of the
Company or any other matter, or any rights whatsoever as shareholders of the
Company.

            (b) In the event the Company intends to make any distribution of its
Common Stock (or other securities which may be issuable in lieu thereof upon the
exercise of the Agent Warrant), including, without limitation, any such
distribution to be made in connection with a consolidation or merger in which
the Company is the continuing corporation, or to issue, offer, or request any
waiver with respect to any subscription rights or warrants to holders of its
Common Stock, the Company shall cause a notice of its intention to make such
distribution to be sent by first-class mail, postage prepaid, at least twenty
(20) days prior to the date fixed as a record date or the date of closing the
transfer books in relation to such distribution, to each registered Holder of
the Agent Warrants at such Holder's address appearing on the Agent Warrant
Register.

      12. Notices. Any notice pursuant to this Agreement to be given or made by
the Holder of any Agent Warrant and/or the holder of any Share to or on the
Company shall be sufficiently given or made if sent by first-class mail,
postage prepaid, addressed as follows or to such other address as the Company
may designate by notice given in accordance with this Section 12, to the
Holders of Agent Warrants and/or the holders of Shares:

Micrus Corporation
495 Clyde Avenue
Mountain View, California 94043
Attn: Mr. J. Todd Derbin, President and CEO

with a copy to:

Weil Gotshal & Manges LLP
2882 Sand Hill Road, Suite 280
Menlo Park, California 94025
Attn: Richard Millard, Esq.; Chris Storey, Esq.

            Notices or demands authorized by this Agreement to be given or made
by the company


                                       8

<PAGE>
to the Holder of any Agent Warrant and/or the holder of any Share shall be
sufficiently given or made (except as otherwise provided in this Agreement) if
sent by first-class mail, postage prepaid, addressed to such Holder or such
holder of Shares at the address of such Holder or such holder of Shares as
shown on the Agent Warrant Register or the books of the Company, as the case
may be. Any such notice to the Agent shall be, addressed as follows or to such
other address as the Agent may designate by notice given in accordance with
this Section 12:

Roberts Mitani Capital, LLC
885 Third Avenue, Suite 2800
New York, New York 10022
Attention: Bruce E. Roberts, Esq.

with a copy to:

Morrison Cohen Singer & Weinstein, LLP
750 Lexington Avenue
New York, New York
Attention: Henry A. Singer, Esq.

          13. Binding Effect; Successors and Assigns. The terms and provisions
of this Agreement and the respective rights and obligations of the parties
hereunder shall be binding upon the respective successors and assigns, and
inure to the benefit of, their respective permitted successors and assigns,
including without limitation any entity that acquires all or substantially all
of the assets of the Company or which is the surviving entity in a merger or
consolidation with the Company.

          14.  Governing Law. This Agreement and each Agent Warrant issued
hereunder shall be governed by and construed in accordance with the substantive
laws of the State of California. The Company hereby agrees to accept service of
process by notice given to it pursuant to the provisions of Section 12.

          15.  Counterparts. This Agreement may be executed in any number of
counterparts, each of which so executed shall be deemed to be an original; but
such counterparts together shall constitute but one and the same instrument.

          16.  Supplements. The parties may hereafter enter into an agreement
or other instrument supplemental hereto and which thereafter shall form a part
hereof to provide for the issuance of additional warrants hereunder. All
supplements, amendments and modifications to this agreement shall be in writing
and executed by the parties hereto.



                       [SIGNATURE PAGE FOLLOWS THIS PAGE]




                                       9
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be duly executed as of the day, month and year first above written.


                                       MICRUS CORPORATION


                                       By: /s/ J. Todd Derbin
                                           ------------------------------------
                                           J. Todd Derbin
                                           President & CEO

Attest: [Illegible]
        ----------------------


                                       ROBERTS MITANI CAPITAL, LLC


                                       By: /s/ Bruce E. Roberts
                                           ------------------------------------


Attest: [Illegible]
        ----------------------







                                       10
<PAGE>
                                   EXHIBIT A

                   VOID AFTER 5:00 P.M. EASTERN STANDARD TIME

                              ON DECEMBER 11, 2005

Title:

THIS WARRANT AND THE SECURITIES ISSUABLE UPON THE EXERCISE HEREOF HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933. THEY MAY NOT BE SOLD, OFFERED FOR
SALE, PLEDGED, HYPOTHECATED, OR OTHERWISE TRANSFERRED EXCEPT PURSUANT TO AN
EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933, OR AN
OPINION OF COUNSEL SATISFACTORY TO THE COMPANY THAT REGISTRATION IS NOT REQUIRED
UNDER SUCH ACT OR UNLESS SOLD PURSUANT TO RULE 144 UNDER SUCH ACT.

                    WARRANT TO PURCHASE CLASS A COMMON STOCK
                                       OF
                               MICRUS CORPORATION

NO:                                                               377,142 SHARES

     This Warrant is issued to Roberts Mitani Capital, LLC ("RMC"), or its
registered assigns ("Holder"), by Micrus Corporation, a Delaware corporation
(the "Company"), on December 11, 2000 (the "Warrant Issue Date"). This Warrant
(the "Warrant") is issued pursuant to the terms of that certain Warrant
Agreement between the Company and RMC dated December 11, 2000 (the "Warrant
Agreement") as provided for in the Engagement Agreement between Company and RMC
dated March 24, 2000, as amended April 30, 2000 (the "Engagement Agreement").

     1.   Purchase of Shares. Subject to the terms and conditions hereinafter
set forth and set forth in the Purchase Agreement, the Holder is entitled, upon
surrender of this Warrant at the principal office of the Company (or at such
other place as the Company shall notify the holder hereof in writing),
to purchase from the Company up to 377,142 fully paid and nonassessable shares
(the "Warrant Shares") of Class A Common Stock of the Company ("Common Stock").

     2.   Exercise Price. The purchase price for the Warrant Shares shall be
$3.84 per share. Such price shall be subject to adjustment pursuant to Section 8
hereof (such price, as adjusted from time to time, is herein referred to as the
"Exercise Price").

     3.   Exercise Period. This Warrant shall be exercisable, in whole or in
part, on the date of its issuance, and it shall remain so exercisable until 5:00
p.m., Eastern Standard Time, on, December 11, 2005 (the "Warrant Expiration
Date").


                                       11


<PAGE>
     4.   Method of Exercise. While this Warrant remains outstanding and
exercisable in accordance with Section 3 above, the Holder may exercise, in
whole or in part, the purchase rights evidenced hereby. Such exercise shall be
effected by:

          (a)  the surrender of the Warrant, together with a duly executed copy
of the form of Notice of Election attached hereto, to the Secretary of the
Company at its principal offices; and

          (b)  the payment to the Company of an amount equal to the aggregate
Exercise Price for the number of Warrant Shares being purchased.

     5.   Net Exercise. In lieu of exercising this Warrant pursuant to Section
4, the Holder may elect to receive, without the payment by the Holder of any
additional consideration, shares of Common Stock equal to the value of this
Warrant (or the portion thereof being canceled) by surrender of this Warrant at
the principal office of the Company together with notice of such election, in
which event the Company shall issue to the holder hereof a number of shares of
Common Stock computed using the following formula:

              Y(A-B)
          X = ------
                A

Where:    X=   The number of shares of Common Stock to be issued to the Holder
               pursuant to this net exercise;

          Y=   The number of Warrant Shares in respect of which the net issue
               election is made,

          A=   The Fair Market Value of one share of the Common Stock at the
               time the net issue election is made;

          B=   The Exercise Price (as adjusted to the date of the net issuance).

For purposes of this Section 5, the Fair Market Value of one share of Common
Stock as of a particular date shall be as determined pursuant to Section 4(b) of
the Warrant Agreement; provided, that, if the Warrant is being exercised upon
the closing of the Company's initial public offering, the value will be the
initial "Price to Public" of one share of Common Stock (issuable upon conversion
of such Preferred Stock) specified in the final prospectus with respect to such
offering.

     6.   Certificates for Warrant Shares. Upon the exercise of the purchase
rights evidenced by this Warrant, one or more certificates for the number of
Warrant Shares so purchased shall be issued as soon as practicable thereafter
(with appropriate restrictive legends, if applicable), and in any event within
thirty (30) days of the delivery of the notice of exercise.

     7.   Issuance of Shares. The Company covenants that the Warrant Shares,
when issued pursuant to the exercise of this Warrant, will be duly and validly
issued, fully paid and nonassessable.

                                       12


<PAGE>
      8. Adjustment of Exercise Price and Number of Shares. The number of and
kind of securities purchasable upon exercise of this Warrant and the Exercise
Price shall be subject to adjustment from time to time as follows:

            (a) Subdivisions, Combinations and Other Issuances. If the Company
shall at any time prior to the expiration of this Warrant subdivide its Common
Stock, by split-up or otherwise, or combine its Common Stock, or issue
additional shares of its Preferred Stock or Common Stock (or rights, options or
warrants or convertible or exchangeable securities containing the right to
subscribe for or purchase shares of Common Stock) as a dividend with respect to
any shares of its Common Stock, the number of Warrant Shares issuable on the
exercise of this Warrant shall forthwith be proportionately increased in the
case of a subdivision or stock dividend, or proportionately decreased in the
case of a combination. Appropriate adjustments shall also be made to the
purchase price payable per share, but the aggregate purchase price payable for
the total number of Warrant Shares purchasable under this Warrant (as adjusted)
shall remain the same. Any adjustment under this Section 8(a) shall become
effective at the close of business on the date the subdivision or combination
becomes effective, or as of the record date of such dividend, or in the event
that no record date is fixed, upon the making of such dividend.

            (b) Reclassification, Reorganization and Consolidation. In case of
any reclassification, capital reorganization, or change in the Common Stock of
the Company (other than as a result of a subdivision, combination, or stock
dividend provided for in Section 8(a) above then, as a condition of such
reclassification, reorganization, or change, lawful provision shall be made, and
duly executed documents evidencing the same from the Company or its successor
shall be delivered to the Holder, so that the Holder shall have the right at any
time prior to the expiration of this Warrant to purchase, at a total price equal
to that payable upon the exercise of this Warrant, the kind and amount of shares
of stock and other securities and property receivable in connection with such
reclassification, reorganization, or change by a holder of the same number of
shares of Common Stock as were purchasable by the Holder immediately prior to
such reclassification, reorganization, or change. Such reclassification,
reorganization and consolidation may include without limitation a transfer of
Company's assets to an affiliate company to be formed under the laws of
Switzerland or similar entity. In any such case, appropriate provisions shall be
made with respect to the rights and interest of the Holder so that the
provisions hereof shall thereafter be applicable with respect to any shares of
stock or other securities and property deliverable upon exercise hereof, and
appropriate adjustments shall be made to the purchase price per share payable
hereunder, provided the aggregate purchase price shall remain the same.

            (c) Notice of Adjustment. When any adjustment is required to be made
in the number or kind of shares purchasable upon exercise of the Warrant, or in
the Exercise Price, the Company shall promptly notify the holder of such event
and of the number of shares of Preferred Stock or other securities or property
thereafter purchasable upon exercise of this Warrant.

      9. No Fractional Shares or Scrip. No fractional shares or scrip
representing fractional shares shall be issued upon the exercise of this
Warrant, but in lieu of such fractional shares


                                       13
<PAGE>
the Company shall make a cash payment therefor on the basis of the Exercise
Price then in effect.

          10.  No Stockholder Rights.  Prior to exercise of this Warrant, the
Holder shall not be entitled to any rights of a stockholder with respect to the
Warrant Shares, including (without limitation) the right to vote such Warrant
Shares, receive dividends or other distributions thereon, exercise preemptive
rights or be notified of stockholder meetings, and such holder shall not be
entitled to any notice or other communication concerning the business or
affairs of the Company. However, nothing in this Section 10 shall limit the
right of the Holder to be provided the notices required under this Warrant as
provided in Section 15 hereto or the Warrant Agreement as provided therein.

          11.  Transfers of Warrant.  Subject to compliance with applicable
federal and state securities laws, this Warrant and all rights hereunder are
transferable in whole or in part by the Holder to any person or entity upon
written notice to the Company; provided, however, that to the extent the
transferee is not a party to the Company's Amended and Restated Stockholders'
Agreement dated August   , 2000, as amended from time to time (the
"Stockholders' Agreement"), such transfer shall be further subject to such
transferee agreeing in writing that upon exercise of this Warrant such
transferee and the Warrant Shares issued upon exercise of this Warrant will be
subject to the Stockholders' Agreement. The transfer shall be recorded on the
books of the Company upon the surrender of this Warrant, properly endorsed, to
the Company at its principal offices, and the payment to the Company of all
transfer taxes and other governmental charges imposed on such transfer. In the
event of a partial transfer, the Company shall issue to the holders one or more
appropriate new warrants.

          13.  Successors and Assigns.  The terms and provisions of this Warrant
and the Purchase Agreement shall inure to the benefit of, and be binding upon,
the Company and the Holders hereof and their respective successors and assigns.

          14.  Amendments and Waivers.  Any term of this Warrant may be amended
and the observance of any term of this Warrant may be waived (either generally
or in a particular instance and either retroactively or prospectively), with
the written consent of the Company and the holders of a majority of shares of
Preferred Stock issued or issuable upon exercise of Warrants. Any waiver or
amendment effected in accordance with this Section shall be binding upon each
holder of any Warrant Shares purchased under this Warrant at the time
outstanding (including securities into which such Warrant Shares have been
converted), each future holder of all such Warrant Shares, and the Company.

          15.  Notices.  All notices required under this Warrant and shall be
deemed to have been given or made for all purposes (a) upon personal delivery,
(b) upon confirmation receipt that the communication was successfully sent to
the applicable number if sent by facsimile; (c) one day after being sent, when
sent by professional overnight courier service, or (d) five days after posting
when sent by registered or certified mail. Notices to the Company shall be sent
to the principal office of the Company (or at such other place as the Company
shall notify the Holder hereof in writing). Notices to the Holder shall be sent
to the address of the Holder on the books of the Company (or at such other
place as the Holder shall notify the Company hereof in writing).


                                       14
<PAGE>
     16.  Attorney's Fees. If any action of law or equity is necessary to
enforce or interpret the terms of this Warrant, the prevailing party shall be
entitled to its reasonable attorneys' fees, costs and disbursements in addition
to any other relief to which it may be entitled.

     17.  Captions. The section and subsection headings of this Warrant are
inserted for convenience only and shall not constitute a part of this Warrant
in construing or interpreting any provision hereof.

     18.  Governing Law. This Warrant shall be governed by the laws of the
State of California as applied to agreements among California residents made
and to be performed entirely within the State of California.

                       [SIGNATURE PAGE FOLLOWS THIS PAGE]






                                       15
<PAGE>
     IN WITNESS WHEREOF, Micrus Corporation has caused this Warrant to be
executed by an officer thereunto duly authorized.


                                                  /s/ J. Todd Derbin
                                             ----------------------------
                                             By: J. Todd Derbin
                                                 President and CEO










                                       16

<PAGE>
                               NOTICE OF EXERCISE
                               ------------------

To: MICRUS CORPORATION

          The undersigned hereby elects to:

--------  (a)  Purchase ------------- shares of Series A Common Stock of Micrus
               Corporation, pursuant to the terms of the attached Warrant and
               payment of the Exercise Price per share required under such
               Warrant accompanies this notice;

          OR

--------  (b)  Exercise the attached Warrant for [all of the shares] [----------
               of the shares] purchasable under the Warrant pursuant to the net
               exercise provisions of Section 5 of such Warrant.

          The undersigned hereby represents and warrants that the undersigned
is acquiring such shares for its own account for investment purposes only, and
not for resale or with a view to distribution of such shares or any part
thereof.

                                        ROBERTS MITANI CAPITAL, LLC:

                                        By: --------------------------------

                                             Name:
                                             Title:



                                        Address:

                                        ------------------------------------


                                        ------------------------------------

                                        Date: ------------------------------

                                        Name in which shares should be
                                        registered:


                                        ------------------------------------





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