<PAGE> PAGE 1
000 B000000 12/31/1999
000 C000000 0000812195
000 D000000 N
000 E000000 NF
000 F000000 Y
000 G000000 N
000 H000000 N
000 I000000 6.1
000 J000000 A
001 A000000 PIONEER MONEY MARKET TRUST
001 B000000 811-05099
001 C000000 6177427825
002 A000000 60 STATE STREET
002 B000000 BOSTON
002 C000000 MA
002 D010000 02109
002 D020000 1820
003 000000 N
004 000000 N
005 000000 N
006 000000 N
007 A000000 Y
007 B000000 1
007 C010100 1
007 C020100 PIONEER CASH RESERVES FUND
007 C030100 N
007 C010200 2
007 C010300 3
007 C010400 4
007 C010500 5
007 C010600 6
007 C010700 7
007 C010800 8
007 C010900 9
007 C011000 10
008 A00AA01 PIONEER INVESTMENT MANAGEMENT, INC.
008 B00AA01 A
008 C00AA01 801-8255
008 D01AA01 BOSTON
008 D02AA01 MA
008 D03AA01 02109
008 D04AA01 1820
010 A00AA01 PIONEER INVESTMENT MANAGEMENT, INC.
010 B00AA01 801-8255
010 C01AA01 BOSTON
010 C02AA01 MA
010 C03AA01 02109
010 C04AA01 1820
011 A00AA01 PIONEER FUNDS DISTRIBUTOR, INC.
011 B00AA01 8-41256
011 C01AA01 BOSTON
<PAGE> PAGE 2
011 C02AA01 MA
011 C03AA01 02109
011 C04AA01 1820
012 A00AA01 PIONEERING SERVICES CORPORATION
012 B00AA01 84-1359
012 C01AA01 BOSTON
012 C02AA01 MA
012 C03AA01 02109
012 C04AA01 1820
013 A00AA01 ARTHUR ANDERSEN LLP
013 B01AA01 BOSTON
013 B02AA01 MA
013 B03AA01 02110
013 B04AA01 2812
015 A00AA01 BROWN BROTHERS HARRIMAN & CO.
015 B00AA01 C
015 C01AA01 BOSTON
015 C02AA01 MA
015 C03AA01 02109
015 C04AA01 1975
015 E01AA01 X
018 00AA00 Y
019 A00AA00 Y
019 B00AA00 37
019 C00AA00 PIONEERFDS
020 C000001 0
020 C000002 0
020 C000003 0
020 C000004 0
020 C000005 0
020 C000006 0
020 C000007 0
020 C000008 0
020 C000009 0
020 C000010 0
021 000000 0
022 A000001 BROWN BROTHERS
022 B000001 13-4973745
022 C000001 9569050
022 D000001 0
022 A000002 GOLDMAN SACHS
022 C000002 485962
022 D000002 0
022 A000003 LUMMIS & COMPANY
022 B000003 06-0909285
022 C000003 350071
022 D000003 8648
022 A000004 EXXON CREDIT CORPORATION
022 B000004 13-3072652
022 C000004 238688
022 D000004 0
<PAGE> PAGE 3
022 A000005 EXXON PROJECT INVEST.
022 C000005 108793
022 D000005 0
022 A000006 LEHMAN BROTHERS
022 B000006 13-2518466
022 C000006 104962
022 D000006 0
022 A000007 AMERICAN EXPRESS
022 B000007 11-1988350
022 C000007 93766
022 D000007 0
022 A000008 CHEVRON OIL FINANCE
022 C000008 86509
022 D000008 0
022 A000009 FORD MOTOR CREDIT
022 B000009 38-1612444
022 C000009 63434
022 D000009 7998
022 A000010 LANSTON, AUBREY G.
022 B000010 13-5552129
022 C000010 70000
022 D000010 0
023 C000000 11949013
023 D000000 23799
024 00AA00 N
025 D00AA01 0
025 D00AA02 0
025 D00AA03 0
025 D00AA04 0
025 D00AA05 0
025 D00AA06 0
025 D00AA07 0
025 D00AA08 0
026 A000000 N
026 B000000 N
026 C000000 N
026 D000000 Y
026 E000000 N
026 F000000 N
026 G010000 N
026 G020000 N
026 H000000 N
027 000000 Y
029 00AA00 N
030 A00AA00 0
030 B00AA00 0.00
030 C00AA00 0.00
031 A00AA00 0
031 B00AA00 0
032 00AA00 0
033 00AA00 0
<PAGE> PAGE 4
045 00AA00 Y
046 00AA00 N
047 00AA00 Y
048 00AA00 0.400
048 A01AA00 0
048 A02AA00 0.000
048 B01AA00 0
048 B02AA00 0.000
048 C01AA00 0
048 C02AA00 0.000
048 D01AA00 0
048 D02AA00 0.000
048 E01AA00 0
048 E02AA00 0.000
048 F01AA00 0
048 F02AA00 0.000
048 G01AA00 0
048 G02AA00 0.000
048 H01AA00 0
048 H02AA00 0.000
048 I01AA00 0
048 I02AA00 0.000
048 J01AA00 0
048 J02AA00 0.000
048 K01AA00 0
048 K02AA00 0.000
054 A00AA00 Y
054 B00AA00 N
054 C00AA00 N
054 D00AA00 N
054 E00AA00 N
054 F00AA00 N
054 G00AA00 N
054 H00AA00 Y
054 I00AA00 N
054 J00AA00 Y
054 K00AA00 N
054 L00AA00 N
054 M00AA00 Y
054 N00AA00 N
054 O00AA00 N
058 A00AA00 N
059 00AA00 Y
060 A00AA00 Y
060 B00AA00 Y
061 00AA00 1000
077 A000000 Y
077 B000000 Y
077 C000000 N
077 D000000 N
077 E000000 N
<PAGE> PAGE 5
077 F000000 N
077 G000000 N
077 H000000 N
077 I000000 N
077 J000000 N
077 K000000 N
077 L000000 N
077 M000000 N
077 N000000 N
077 O000000 N
077 P000000 N
077 Q010000 N
077 Q020000 N
077 Q030000 N
078 000000 N
080 A00AA00 ICI MUTUAL INSURANCE COMPANY
080 B00AA00 NONE
080 C00AA00 25000
081 A00AA00 Y
081 B00AA00 37
082 A00AA00 N
082 B00AA00 0
083 A00AA00 N
083 B00AA00 0
084 A00AA00 N
084 B00AA00 0
085 A00AA00 Y
085 B00AA00 N
086 A010000 0
086 A020000 0
086 B010000 0
086 B020000 0
086 C010000 0
086 C020000 0
086 D010000 0
086 D020000 0
086 E010000 0
086 E020000 0
086 F010000 0
086 F020000 0
028 A010100 177894
028 A020100 821
028 A030100 0
028 A040100 163774
028 B010100 324233
028 B020100 1116
028 B030100 0
028 B040100 234878
028 C010100 157075
028 C020100 1255
028 C030100 0
<PAGE> PAGE 6
028 C040100 159677
028 D010100 151472
028 D020100 1237
028 D030100 0
028 D040100 169798
028 E010100 167048
028 E020100 1205
028 E030100 0
028 E040100 208803
028 F010100 180318
028 F020100 1184
028 F030100 0
028 F040100 166600
028 G010100 1158040
028 G020100 6818
028 G030100 0
028 G040100 1103530
028 H000100 0
034 000100 Y
035 000100 666
036 A000100 N
036 B000100 0
037 000100 N
038 000100 0
039 000100 N
040 000100 Y
041 000100 Y
042 A000100 0
042 B000100 0
042 C000100 0
042 D000100 100
042 E000100 0
042 F000100 0
042 G000100 0
042 H000100 0
043 000100 1161
044 000100 0
049 000100 N
050 000100 N
051 000100 N
052 000100 N
053 A000100 N
055 A000100 N
055 B000100 N
056 000100 Y
057 000100 N
062 A000100 Y
062 B000100 0.0
062 C000100 5.4
062 D000100 16.9
062 E000100 0.0
<PAGE> PAGE 7
062 F000100 0.0
062 G000100 0.0
062 H000100 0.0
062 I000100 78.1
062 J000100 0.0
062 K000100 0.0
062 L000100 0.0
062 M000100 0.0
062 N000100 0.0
062 O000100 0.0
062 P000100 0.0
062 Q000100 0.0
062 R000100 0.0
063 A000100 23
063 B000100 0.0
064 A000100 N
064 B000100 N
066 A000100 N
067 000100 N
068 A000100 N
068 B000100 N
069 000100 N
070 A010100 Y
070 A020100 Y
070 B010100 N
070 B020100 N
070 C010100 N
070 C020100 N
070 D010100 N
070 D020100 N
070 E010100 N
070 E020100 N
070 F010100 N
070 F020100 N
070 G010100 N
070 G020100 N
070 H010100 N
070 H020100 N
070 I010100 N
070 I020100 N
070 J010100 Y
070 J020100 N
070 K010100 N
070 K020100 N
070 L010100 N
070 L020100 N
070 M010100 N
070 M020100 N
070 N010100 N
070 N020100 N
070 O010100 Y
<PAGE> PAGE 8
070 O020100 N
070 P010100 Y
070 P020100 N
070 Q010100 N
070 Q020100 N
070 R010100 N
070 R020100 N
071 A000100 0
071 B000100 0
071 C000100 0
071 D000100 0
072 A000100 12
072 B000100 17988
072 C000100 0
072 D000100 0
072 E000100 0
072 F000100 1393
072 G000100 72
072 H000100 0
072 I000100 848
072 J000100 66
072 K000100 0
072 L000100 33
072 M000100 27
072 N000100 373
072 O000100 0
072 P000100 0
072 Q000100 0
072 R000100 35
072 S000100 10
072 T000100 1161
072 U000100 0
072 V000100 0
072 W000100 9
072 X000100 4027
072 Y000100 0
072 Z000100 13961
072AA000100 0
072BB000100 0
072CC010100 0
072CC020100 0
072DD010100 11160
072DD020100 2801
072EE000100 0
073 A010100 0.0000
073 A020100 0.0000
073 B000100 0.0000
073 C000100 0.0000
074 A000100 65
074 B000100 62600
074 C000100 310150
<PAGE> PAGE 9
074 D000100 0
074 E000100 0
074 F000100 0
074 G000100 0
074 H000100 0
074 I000100 0
074 J000100 0
074 K000100 0
074 L000100 5944
074 M000100 8
074 N000100 378767
074 O000100 0
074 P000100 259
074 Q000100 0
074 R010100 0
074 R020100 0
074 R030100 0
074 R040100 7230
074 S000100 0
074 T000100 371278
074 U010100 287402
074 U020100 84152
074 V010100 0.00
074 V020100 0.00
074 W000100 0.9993
074 X000100 22830
074 Y000100 0
075 A000100 350781
075 B000100 0
076 000100 0.00
SIGNATURE ROBERT P. NAULT
TITLE ASST. SECRETARY
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000812195
<NAME> PIONEER CASH RESERVES FUND
<SERIES>
<NUMBER> 001
<NAME> PIONEER CASH RESERVES FUND CLASS A
<CURRENCY> US
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1999
<PERIOD-END> DEC-31-1999
<EXCHANGE-RATE> 1
<INVESTMENTS-AT-COST> 372749804
<INVESTMENTS-AT-VALUE> 372749804
<RECEIVABLES> 5944520
<ASSETS-OTHER> 8136
<OTHER-ITEMS-ASSETS> 64586
<TOTAL-ASSETS> 378767046
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 7488644
<TOTAL-LIABILITIES> 7488644
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 371554465
<SHARES-COMMON-STOCK> 287402305
<SHARES-COMMON-PRIOR> 250593570
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 276063
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 371278402
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 17988212
<OTHER-INCOME> 0
<EXPENSES-NET> 4027108
<NET-INVESTMENT-INCOME> 13961104
<REALIZED-GAINS-CURRENT> 0
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 13961104
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 11160344
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 1942247005
<NUMBER-OF-SHARES-REDEEMED> 1915279542
<SHARES-REINVESTED> 9841272
<NET-CHANGE-IN-ASSETS> 63006066
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 276063
<GROSS-ADVISORY-FEES> 1392778
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 4189971
<AVERAGE-NET-ASSETS> 268070318
<PER-SHARE-NAV-BEGIN> 1.00
<PER-SHARE-NII> 0.04
<PER-SHARE-GAIN-APPREC> 0
<PER-SHARE-DIVIDEND> 0.04
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.00
<EXPENSE-RATIO> 1.01
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000812195
<NAME> PIONEER CASH RESERVES FUND
<SERIES>
<NUMBER> 002
<NAME> PIONEER CASH RESERVES FUND CLASS B
<CURRENCY> US
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1999
<PERIOD-END> DEC-31-1999
<EXCHANGE-RATE> 1
<INVESTMENTS-AT-COST> 372749804
<INVESTMENTS-AT-VALUE> 372749804
<RECEIVABLES> 5944520
<ASSETS-OTHER> 8136
<OTHER-ITEMS-ASSETS> 64586
<TOTAL-ASSETS> 378767046
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 7488644
<TOTAL-LIABILITIES> 7488644
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 371554465
<SHARES-COMMON-STOCK> 67184355
<SHARES-COMMON-PRIOR> 39638857
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 276063
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 371278402
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 17988212
<OTHER-INCOME> 0
<EXPENSES-NET> 4027108
<NET-INVESTMENT-INCOME> 13961104
<REALIZED-GAINS-CURRENT> 0
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 13961104
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 1818635
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 191889286
<NUMBER-OF-SHARES-REDEEMED> 165933810
<SHARES-REINVESTED> 1590022
<NET-CHANGE-IN-ASSETS> 63006066
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 276063
<GROSS-ADVISORY-FEES> 1392778
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 4189971
<AVERAGE-NET-ASSETS> 54206716
<PER-SHARE-NAV-BEGIN> 1.00
<PER-SHARE-NII> 0.03
<PER-SHARE-GAIN-APPREC> 0
<PER-SHARE-DIVIDEND> 0.03
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.00
<EXPENSE-RATIO> 1.83
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000812195
<NAME> PIONEER CASH RESERVES FUND
<SERIES>
<NUMBER> 003
<NAME> PIONEER CASH RESERVES FUND CLASS C
<CURRENCY> US
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1999
<PERIOD-END> DEC-31-1999
<EXCHANGE-RATE> 1
<INVESTMENTS-AT-COST> 372749804
<INVESTMENTS-AT-VALUE> 372749804
<RECEIVABLES> 5944520
<ASSETS-OTHER> 8136
<OTHER-ITEMS-ASSETS> 64586
<TOTAL-ASSETS> 378767046
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 7488644
<TOTAL-LIABILITIES> 7488644
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 371554465
<SHARES-COMMON-STOCK> 16967805
<SHARES-COMMON-PRIOR> 18315972
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 276063
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 371278402
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 17988212
<OTHER-INCOME> 0
<EXPENSES-NET> 4027108
<NET-INVESTMENT-INCOME> 13961104
<REALIZED-GAINS-CURRENT> 0
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 13961104
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 982125
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 444608185
<NUMBER-OF-SHARES-REDEEMED> 446718522
<SHARES-REINVESTED> 762170
<NET-CHANGE-IN-ASSETS> 63006066
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 276063
<GROSS-ADVISORY-FEES> 1392778
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 4189971
<AVERAGE-NET-ASSETS> 28503846
<PER-SHARE-NAV-BEGIN> 1.00
<PER-SHARE-NII> 0.03
<PER-SHARE-GAIN-APPREC> 0
<PER-SHARE-DIVIDEND> 0.03
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.00
<EXPENSE-RATIO> 1.76
</TABLE>
REPORT OF INDEPENDENT PUBLIC ACCOUNTANTS
To the Board of Trustees of
Pioneer Cash Reserves Fund:
In planning and performing our audit of the financial statements of Pioneer Cash
Reserves Fund for the year ended December 31, 1999, we considered its internal
control, including control activities for safeguarding securities, in order to
determine our auditing procedures for the purpose of expressing our opinion on
the financial statements and to comply with the requirements of Form N-SAR, not
to provide assurance on internal control.
The management of Pioneer Cash Reserves Fund is responsible for establishing and
maintaining internal control. In fulfilling this responsibility, estimates and
judgments by management are required to assess the expected benefits and related
costs of controls. Generally, controls that are relevant to an audit pertain to
the entity's objective of preparing financial statements for external purposes
that are fairly presented in conformity with generally accepted accounting
principles. Those controls include the safeguarding of assets against
unauthorized acquisition, use or disposition.
Because of inherent limitations in internal control, error or fraud may occur
and not be detected. Also, projection of any evaluation of internal control to
future periods is subject to the risk that it may become inadequate because of
changes in conditions or that the effectiveness of the design and operation may
deteriorate.
Our consideration of internal control would not necessarily disclose all matters
in internal control that might be material weaknesses under standards
established by the American Institute of Certified Public Accountants. A
material weakness is a condition in which the design or operation of one or more
of the internal control components does not reduce to a relatively low level the
risk that misstatements caused by error or fraud in amounts that would be
material in relation to the financial statements being audited may occur and not
be detected within a timely period by employees in the normal course of
performing their assigned functions. However, we noted no matters involving
internal control and its operation, including controls for safeguarding
securities, that we consider to be material weaknesses as defined above as of
December 31, 1999.
This report is intended solely for the information and use of management, the
Board of Trustees of Pioneer Cash Reserves Fund, and the Securities and Exchange
Commission.
ARTHUR ANDERSEN LLP
/s/ Arthur Andersen LLP
Boston, Massachusetts
February 4, 2000
