Xybernaut Corporation
                       12701 Fair Lakes Circle, Suite 550
                             Fairfax, Virginia 22033
                               (703) 631-6925 (T)
                               (703) 631-3903 (F)


                                  May 30, 2003

Sundial Investments, Limited
Gretton House
P.O. Box 65, Duke Street
British West Indies
ATTN:  Ms. Beverly Simmons

       Re:   Notice of Warrant Exercise and Satisfaction of Promissory Note
             --------------------------------------------------------------

Gentlemen:

         Reference is made to: (i) that  certain  Promissory  Note,  dated as of
March 26,  2003  (the  "Note"),  issued by  Xybernaut  Corporation,  a  Delaware
corporation  (the  "Company"),  in favor of Sundial  Investments,  Limited  (the
"Investor")  in the initial  principal  amount of  $1,750,000  (which  principal
amount has been previously reduced by the amount of $860,000, with the remaining
principal amount of $890,000  currently  outstanding on the Note), and (ii) that
certain Common Stock Purchase Warrant, Number W-M03-1, dated March 26, 2003 (the
"Warrant"),  exercisable  into 1,750,000  shares of common stock, par value $.01
per share, of the Company  ("Common  Stock"),  at an exercise price of $1.25 per
share (the "Exercise Price"), issued by the Company to the Investor.

         For good and valuable consideration,  the receipt and adequacy of which
is hereby acknowledged, the Company and the Investor hereby agree as follows:

         The Investor agrees to reduce the outstanding  principal  amount of the
Note by ten (10%) percent,  or $89,000,  resulting in an  outstanding  principal
amount on the Note of  $801,000.  The  Investor  agrees to  exercise  all of the
shares  underlying  the Warrant,  and the Company agrees that the Exercise Price
shall be reduced from $1.25 to $0.32 cents per share. The Investor hereby elects
to apply the outstanding principal amount of $560,000 of the Note as payment for
the Exercise Price of the shares of Common Stock underlying the Warrant.

         The  remaining  outstanding  principal  amount of the Note of $241,000,
plus  accrued and unpaid  interest of  $11,229.17,  shall be paid in full by the
Company's  issuance  to the  Investor  of: (i) 651,352  shares  (the  "Principal
Payment  Shares") of Common Stock,  at an agreed upon  valuation  equal to $0.37
cents per share, for the payment of outstanding  principal on the Note, and (ii)
30,349 shares (the "Interest  Payment  Shares" and,  together with the Principal
Payment Shares,  the "Shares") of its Common Stock at a price of $0.37 cents per
share,  for the payment of accrued and unpaid  interest on the Note.  The Shares
shall not be registered with the Securities and Exchange Commission and shall be
"restricted  securities",  within the meaning of Rule 144 promulgated  under the
Securities  Act of 1933, as amended.  If, at any time following 90 days from the
date hereof,  the




Sundial Investments, Limited
May 30, 2003
Page -2-

Company files a registration  statement on Form S-3 (or other  appropriate  form
then available,  except on Form S-4, S-8 or their respective successor forms) in
connection with a public or private offering of its securities to investors, the
Company  shall  include the Shares which are being issued by the Company on such
registration statement.

         The  Investor  represents  and  warrants to the  Company  that it is an
"accredited" investor, as that term is defined in Rule 501 of the Securities Act
and it is acquiring  the Shares for  investment  purposes and not with a view to
the distribution of the Shares to the public.

         Upon our execution of this letter agreement, any and all obligations of
the Company to the Investor  under the Note shall be fully  satisfied,  the Note
shall be  terminated  and marked  "paid in full" and the  Investor  will have no
remaining rights, powers, privileges, remedies or interests under the Note.

         As promptly as  practicable  but no later than three (3) business  days
following the exercise of the Warrant, the Company shall take such actions as it
shall deem necessary or appropriate to deliver the final prospectus,  as amended
or  supplemented,  relating to the sale of the shares of Common Stock underlying
the Warrant under the Securities Act of 1933, as amended and deliver same to the
Investor prior to sale. The Investor agrees that it shall not sell any shares of
Common Stock underlying the Warrant  pursuant to the  Registration  Statement on
Form S-3,  Registration  No.  333-104223,  without proper  delivery of the final
prospectus, as amended or supplemented.

         Except as  amended  hereby,  the  provisions  of the  Warrant  shall be
unmodified and shall remain in full force and effect.

         Please  confirm  your  agreement  to the  foregoing  by  executing  the
enclosed copy of this letter and returning it to the  undersigned,  whereupon it
shall become a binding agreement between us as of the date hereof.

                                     Very truly yours,

                                     XYBERNAUT CORPORATION

                                     By:
                                         --------------------------------
                                         Name:
                                         Title:

AGREED:

SUNDIAL INVESTMENTS, LIMITED

By:
   -----------------------------------
Name:
Title: