**MICROMUSE INC.**

**Exhibit 99.1**

CERTIFICATION OF PRINCIPAL EXECUTIVE OFFICERPURSUANT TO 18 U.S.C. SECTION 1350

In connection with the accompanying Quarterly Report on Form 10-Q ofMicromuse Inc. for the quarter ended June 30, 2002, I, Gregory Q. Brown, Chairman and Chief Executive Officer of Micromuse Inc., hereby certify pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002,to the best of my knowledge and belief, that:

| (1)    |   | such Quarterly Report on Form 10-Q for the quarter ended June 30, 2002, fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of1934; and                                  |
|--------|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |
| (2)    |   | the information contained in such Quarterly Report on Form 10-Q for the quarter ended June 30, 2002, fairly presents, in all material respects, the financial condition and resultsof operations of Micromuse Inc. |

|   |                                   |
|--------|----------------------------------------|
|   |                                   |
|   | By: /s/ GREGORY Q. BROWN               |
|   | Gregory Q. Brown                       |
|   | *Chairman and Chief Executive Officer* |
|   |                                   |
|   |                                   |
|   |                                   |

CERTIFICATION OF PRINCIPAL FINANCIAL OFFICERPURSUANT TO 18 U.S.C. SECTION 1350

In connection with the accompanying Quarterly Report on Form 10-Q of Micromuse Inc. for the quarter ended June 30, 2002, I, Michael L. Luetkemeyer, Senior Vice President and Chief Financial Officerof Micromuse Inc., hereby certify pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, to the best of my knowledge and belief, that:

| (1)    |   | such Quarterly Report on Form 10-Q for the quarter ended June 30, 2002, fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of1934; and                                  |
|--------|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |
| (2)    |   | the information contained in such Quarterly Report on Form 10-Q for the quarter ended June 30, 2002, fairly presents, in all material respects, the financial condition and resultsof operations of Micromuse Inc. |

|   |                                                                                                                                                                                                        |
|--------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|   |                                                                                                                                                                                                        |
|   | By: /s/ MICHAEL L.LUETKEMEYER                              |
|   | Michael L. Luetkemeyer                                                                                                                                                                                      |
|   | *Senior Vice President and Chief Financial Officer*                                                                                                                                                         |

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