EX-99. CERT


                  CERTIFICATION PURSUANT TO SECTION 302
                    OF THE SARBANES-OXLEY ACT OF 2002


I, Robert C. Doll, Jr., Chief Executive Officer of CMA Tax-Exempt Fund and
Master Tax-Exempt Trust, certify that:

1. I have reviewed this report on Form N-CSR of CMA Tax-Exempt Fund and Master
   Tax-Exempt Trust;

2. Based on my knowledge, this report does not contain any untrue statement of
   a material fact or omit to state a material fact necessary to make the
   statements made, in light of the circumstances under which such statements
   were made, not misleading with respect to the period covered by this
   report;

3. Based on my knowledge, the financial statements, and other financial
   information included in this report, fairly present in all material
   respects the financial condition, results of operations, changes in net
   assets, and cash flows (if the financial statements are required to include
   a statement of cash flows) of the registrants as of, and for, the periods
   presented in this report;

4. The registrants' other certifying officer(s) and I are responsible for
   establishing and maintaining disclosure controls and procedures (as defined
   in Rule 30a-3(c) under the Investment Company Act of 1940) and internal
   control over financial reporting (as defined in Rule 30a-3(d) under the
   Investment Company Act of 1940) for the registrants and have:

a) designed such disclosure controls and procedures, or caused such disclosure
   controls and procedures to be designed under our supervision, to ensure
   that material information relating to the registrant, including its
   consolidated subsidiaries, is made known to us by others within those
   entities, particularly during the period in which this report is being
   prepared;

b) designed such internal control over financial reporting, or caused such
   internal control over financial reporting to be designed under our
   supervision, to provide reasonable assurance regarding the reliability of
   financial reporting and the preparation of financial statements for
   external purposes in accordance with generally accepted accounting
   principles;

c) evaluated the effectiveness of the registrants' disclosure controls and
   procedures and presented in this report our conclusions about the
   effectiveness of the disclosure controls and procedures, as of a date
   within 90 days prior to the filing date of this report based on such
   evaluation; and

d) disclosed in this report any change in the registrants' internal control
   over financial reporting that occurred during the second fiscal quarter of
   the period covered by this report that has materially affected, or is
   reasonably likely to materially affect, the registrants' internal control
   over financial reporting; and

5. The registrants' other certifying officer(s) and I have disclosed to the
   registrants' auditors and the audit committee of the registrants' board of
   directors (or persons performing the equivalent functions):

a) all significant deficiencies and material weaknesses in the design or
   operation of internal control over financial reporting which are reasonably
   likely to adversely affect the registrant's ability to record, process,
   summarize, and report financial information; and

b) any fraud, whether or not material, that involves management or other
   employees who have a significant role in the registrants' internal control
   over financial reporting.


Date: November 17, 2005


                                         /s/ Robert C. Doll, Jr.
                                         ------------------------
                                         Robert C. Doll, Jr.,
                                         Chief Executive Officer of
                                         CMA Tax-Exempt Fund and
                                         Master Tax-Exempt Trust



EX-99. CERT


                  CERTIFICATION PURSUANT TO SECTION 302
                    OF THE SARBANES-OXLEY ACT OF 2002



I, Donald C. Burke, Chief Financial Officer of CMA Tax-Exempt Fund and Master
Tax-Exempt Trust, certify that:

1. I have reviewed this report on Form N-CSR of CMA Tax-Exempt Fund and Master
   Tax-Exempt Trust;

2. Based on my knowledge, this report does not contain any untrue statement of
   a material fact or omit to state a material fact necessary to make the
   statements made, in light of the circumstances under which such statements
   were made, not misleading with respect to the period covered by this
   report;

3. Based on my knowledge, the financial statements, and other financial
   information included in this report, fairly present in all material
   respects the financial condition, results of operations, changes in net
   assets, and cash flows (if the financial statements are required to include
   a statement of cash flows) of the registrants as of, and for, the periods
   presented in this report;

4. The registrants' other certifying officer(s) and I are responsible for
   establishing and maintaining disclosure controls and procedures (as defined
   in Rule 30a-3(c) under the Investment Company Act of 1940) and internal
   control over financial reporting (as defined in Rule 30a-3(d) under the
   Investment Company Act of 1940) for the registrants and have:

a) designed such disclosure controls and procedures, or caused such disclosure
   controls and procedures to be designed under our supervision, to ensure
   that material information relating to the registrant, including its
   consolidated subsidiaries, is made known to us by others within those
   entities, particularly during the period in which this report is being
   prepared;

b) designed such internal control over financial reporting, or caused such
   internal control over financial reporting to be designed under our
   supervision, to provide reasonable assurance regarding the reliability of
   financial reporting and the preparation of financial statements for
   external purposes in accordance with generally accepted accounting
   principles;

c) evaluated the effectiveness of the registrants' disclosure controls and
   procedures and presented in this report our conclusions about the
   effectiveness of the disclosure controls and procedures, as of a date
   within 90 days prior to the filing date of this report based on such
   evaluation; and

d) disclosed in this report any change in the registrants' internal control
   over financial reporting that occurred during the second fiscal quarter of
   the period covered by this report that has materially affected, or is
   reasonably likely to materially affect, the registrants' internal control
   over financial reporting; and

5. The registrants' other certifying officer(s) and I have disclosed to the
   registrants' auditors and the audit committee of the registrants' board of
   directors (or persons performing the equivalent functions):

a) all significant deficiencies and material weaknesses in the design or
   operation of internal control over financial reporting which are reasonably
   likely to adversely affect the registrant's ability to record, process,
   summarize, and report financial information; and

b) any fraud, whether or not material, that involves management or other
   employees who have a significant role in the registrants' internal control
   over financial reporting.


Date: November 17, 2005


                                         /s/ Donald C. Burke
                                         --------------------
                                         Donald C. Burke,
                                         Chief Financial Officer of
                                         CMA Tax-Exempt Fund and
                                         Master Tax-Exempt Trust