<PAGE> PAGE 1
000 B000000 12/31/1999
000 C000000 1026598
000 D000000 N
000 E000000 NF
000 F000000 Y
000 G000000 N
000 H000000 N
000 I000000 6.1
000 J000000 A
001 A000000 MERRIMAC MASTER PORTFOLIO
001 B000000 811-07941
001 C000000 8099492001
002 A000000 CARDINAL AVENUE P.O. BOX 501
002 B000000 GEORGETOWN
002 E010000 CAYMAN ISLANDS
002 E020000 BWI
003 000000 N
004 000000 N
005 000000 N
006 000000 N
007 A000000 Y
007 B000000 4
007 C010100 1
007 C020100 MERRIMAC CASH PORTFOLIO
007 C030100 N
007 C010200 2
007 C020200 MERRIMAC TREASURY PORTFOLIO
007 C030200 N
007 C010300 3
007 C020300 MERRIMAC TREASURY PLUS PORTFOLIO
007 C030300 N
007 C010400 4
007 C020400 MERRIMAC U.S. GOVERNMENT PORTFOLIO
007 C030400 N
007 C010500 5
007 C010600 6
007 C010700 7
007 C010800 8
007 C010900 9
007 C011000 10
010 A00AA01 IBT TRUST & CUSTODIAL SERVICES (IRELAND) LTD
010 C01AA01 DUBLIN
010 C05AA01 IRELAND
012 A00AA01 IBT FUND SERVICES (CANADA) INC.
012 B00AA01 85-n/a
012 C01AA01 TORONTO, CANADA
012 C02AA01 CA
012 C03AA01 00000
013 A00AA01 ERNST & YOUNG L.L.P.
013 B01AA01 BOSTON
013 B02AA01 MA
<PAGE> PAGE 2
013 B03AA01 02116
015 A00AA01 INVESTORS BANK & TRUST COMPANY
015 B00AA01 C
015 C01AA01 BOSTON
015 C02AA01 MA
015 C03AA01 02116
015 E01AA01 X
018 00AA00 Y
019 A00AA00 Y
019 B00AA00 11
019 C00AA00 MERRIMAC--
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 MERRILL LYNCH PIERCE FENNER & SMITH
022 B000001 13-5674085
022 C000001 17165051
022 D000001 119644
022 A000002 MORGAN STANLEY & CO.
022 B000002 13-2655998
022 C000002 16634519
022 D000002 31198
022 A000003 GOLDMAN SACHS
022 B000003 13-5108880
022 C000003 10170948
022 D000003 573750
022 A000004 LEHMAN BROTHERS
022 B000004 13-2518466
022 C000004 8937531
022 D000004 100240
022 A000005 BEAR STEARNS
022 B000005 13-3299429
022 C000005 6323068
022 D000005 94617
022 A000006 LUMMIS & CO.
022 C000006 5545300
022 D000006 0
022 A000007 CHASE MANHATTAN SECURITIES
022 C000007 2362755
022 D000007 230085
022 A000008 SALOMON SMITH BARNEY
022 B000008 13-5365580
022 C000008 1904862
<PAGE> PAGE 3
022 D000008 412055
022 A000009 PAINEWEBBER
022 B000009 13-3235334
022 C000009 1864639
022 D000009 294614
022 A000010 FIRST BOSTON
022 B000010 13-5659485
022 C000010 1641971
022 D000010 153224
023 C000000 78868861
023 D000000 3913244
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
034 00AA00 N
035 00AA00 0
036 B00AA00 0
037 00AA00 N
038 00AA00 0
039 00AA00 N
040 00AA00 N
041 00AA00 N
042 A00AA00 0
042 B00AA00 0
042 C00AA00 0
042 D00AA00 0
042 E00AA00 0
042 F00AA00 0
042 G00AA00 0
042 H00AA00 0
043 00AA00 0
044 00AA00 0
045 00AA00 Y
046 00AA00 N
047 00AA00 Y
048 00AA00 0.170
<PAGE> PAGE 4
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
049 00AA00 N
050 00AA00 N
051 00AA00 N
052 00AA00 N
053 A00AA00 N
054 A00AA00 Y
054 B00AA00 Y
054 C00AA00 Y
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 Y
054 M00AA00 N
054 N00AA00 N
054 O00AA00 Y
055 A00AA00 N
055 B00AA00 N
056 00AA00 Y
057 00AA00 N
058 A00AA00 N
058 B00AA00 N
058 C00AA00 N
058 D00AA00 N
058 E00AA00 N
<PAGE> PAGE 5
059 00AA00 Y
060 A00AA00 Y
060 B00AA00 Y
061 00AA00 0
066 A00AA00 N
067 00AA00 N
068 A00AA00 N
068 B00AA00 N
069 00AA00 N
077 A000000 Y
077 B000000 Y
078 000000 N
080 A00AA00 NATIONAL UNION FIRE INSURANCE COMPANY
080 C00AA00 2000
081 A00AA00 Y
081 B00AA00 7
082 A00AA00 Y
082 B00AA00 5
083 A00AA00 N
083 B00AA00 0
084 A00AA00 N
084 B00AA00 0
085 A00AA00 Y
085 B00AA00 N
008 A000101 INVESTORS BANK & TRUST COMPANY
008 B000101 A
008 C000101 801-n/a
008 D010101 BOSTON
008 D020101 MA
008 D030101 02116
008 A000102 ALLMERICA ASSET MANAGEMENT, INC.
008 B000102 S
008 C000102 801-44189
008 D010102 WORCESTER
008 D020102 MA
008 D030102 01653
024 000100 Y
025 A000101 LEHMAN BROTHERS HOLDINGS
025 B000101 13-2518466
025 C000101 D
025 D000101 49565
025 A000102 BEAR STEARNS & CO.
025 B000102 13-3299429
025 C000102 D
025 D000102 45014
025 A000103 PAINEWEBBER
025 B000103 13-3235334
025 C000103 D
025 D000103 43839
025 A000104 GOLDMAN SACHS GROUP
025 B000104 13-5108880
<PAGE> PAGE 6
025 C000104 D
025 D000104 38000
025 A000105 MORGAN STANLEY DEAN WITTER
025 B000105 13-2655998
025 C000105 D
025 D000105 4002
025 D000106 0
025 D000107 0
025 D000108 0
028 A010100 646622
028 A020100 0
028 A030100 0
028 A040100 414059
028 B010100 466365
028 B020100 0
028 B030100 0
028 B040100 472353
028 C010100 305041
028 C020100 0
028 C030100 0
028 C040100 264064
028 D010100 270380
028 D020100 0
028 D030100 0
028 D040100 481657
028 E010100 227766
028 E020100 0
028 E030100 0
028 E040100 498301
028 F010100 658529
028 F020100 0
028 F030100 0
028 F040100 575234
028 G010100 2574703
028 G020100 0
028 G030100 0
028 G040100 2705668
028 H000100 0
062 A000100 Y
062 B000100 0.0
062 C000100 0.0
062 D000100 0.0
062 E000100 0.0
062 F000100 13.1
062 G000100 0.0
062 H000100 0.0
062 I000100 27.2
062 J000100 4.5
062 K000100 0.0
062 L000100 59.8
062 M000100 0.0
<PAGE> PAGE 7
062 N000100 0.0
062 O000100 0.0
062 P000100 0.0
062 Q000100 0.0
062 R000100 0.0
063 A000100 68
063 B000100 0.0
064 A000100 N
064 B000100 N
070 A010100 Y
070 A020100 N
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 Y
070 K010100 Y
070 K020100 N
070 L010100 Y
070 L020100 Y
070 M010100 N
070 M020100 N
070 N010100 Y
070 N020100 N
070 O010100 Y
070 O020100 N
070 P010100 N
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 66352
<PAGE> PAGE 8
072 C000100 0
072 D000100 0
072 E000100 0
072 F000100 2118
072 G000100 0
072 H000100 0
072 I000100 0
072 J000100 0
072 K000100 0
072 L000100 0
072 M000100 43
072 N000100 0
072 O000100 0
072 P000100 0
072 Q000100 0
072 R000100 34
072 S000100 69
072 T000100 0
072 U000100 12
072 V000100 0
072 W000100 122
072 X000100 2398
072 Y000100 0
072 Z000100 63954
072AA000100 0
072BB000100 145
072CC010100 0
072CC020100 0
072DD010100 0
072DD020100 0
072EE000100 0
073 A010100 0.0000
073 A020100 0.0000
073 B000100 0.0000
073 C000100 0.0000
074 A000100 593
074 B000100 0
074 C000100 1131625
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 9575
074 M000100 51
074 N000100 1141844
074 O000100 60132
074 P000100 154
<PAGE> PAGE 9
074 Q000100 0
074 R010100 0
074 R020100 0
074 R030100 0
074 R040100 65
074 S000100 0
074 T000100 1081493
074 U010100 0
074 U020100 0
074 V010100 0.00
074 V020100 0.00
074 W000100 0.0000
074 X000100 3
074 Y000100 60132
075 A000100 1245261
075 B000100 0
076 000100 0.00
008 A000201 INVESTORS BANK & TRUST COMPANY
008 B000201 A
008 C000201 801-n/a
008 D010201 BOSTON
008 D020201 MA
008 D030201 02116
008 A000202 M & I INVESTMENT MANAGEMENT CORP.
008 B000202 S
008 C000202 801-9118
008 D010202 MILWAUKEE
008 D020202 WI
008 D030202 53202
024 000200 N
028 A010200 43855
028 A020200 0
028 A030200 0
028 A040200 78201
028 B010200 51494
028 B020200 0
028 B030200 0
028 B040200 31876
028 C010200 43555
028 C020200 0
028 C030200 0
028 C040200 30479
028 D010200 37368
028 D020200 0
028 D030200 0
028 D040200 49838
028 E010200 18102
028 E020200 0
028 E030200 0
028 E040200 45831
028 F010200 70056
<PAGE> PAGE 10
028 F020200 0
028 F030200 0
028 F040200 61284
028 G010200 264430
028 G020200 0
028 G030200 0
028 G040200 297509
028 H000200 0
062 A000200 Y
062 B000200 92.5
062 C000200 0.0
062 D000200 0.0
062 E000200 0.0
062 F000200 0.0
062 G000200 0.0
062 H000200 0.0
062 I000200 0.0
062 J000200 0.0
062 K000200 0.0
062 L000200 6.6
062 M000200 0.0
062 N000200 0.0
062 O000200 0.0
062 P000200 0.0
062 Q000200 0.0
062 R000200 0.0
063 A000200 24
063 B000200 0.0
064 A000200 N
064 B000200 N
070 A010200 N
070 A020200 N
070 B010200 N
070 B020200 N
070 C010200 N
070 C020200 N
070 D010200 N
070 D020200 N
070 E010200 N
070 E020200 N
070 F010200 N
070 F020200 N
070 G010200 N
070 G020200 N
070 H010200 N
070 H020200 N
070 I010200 N
070 I020200 N
070 J010200 Y
070 J020200 N
070 K010200 Y
<PAGE> PAGE 11
070 K020200 Y
070 L010200 N
070 L020200 N
070 M010200 N
070 M020200 N
070 N010200 Y
070 N020200 N
070 O010200 Y
070 O020200 N
070 P010200 N
070 P020200 N
070 Q010200 N
070 Q020200 N
070 R010200 N
070 R020200 N
071 A000200 0
071 B000200 0
071 C000200 0
071 D000200 0
072 A000200 12
072 B000200 7917
072 C000200 443
072 D000200 0
072 E000200 0
072 F000200 303
072 G000200 0
072 H000200 0
072 I000200 0
072 J000200 0
072 K000200 0
072 L000200 0
072 M000200 9
072 N000200 0
072 O000200 0
072 P000200 0
072 Q000200 0
072 R000200 28
072 S000200 5
072 T000200 0
072 U000200 2
072 V000200 0
072 W000200 34
072 X000200 381
072 Y000200 0
072 Z000200 7978
072AA000200 0
072BB000200 4
072CC010200 0
072CC020200 0
072DD010200 0
072DD020200 0
<PAGE> PAGE 12
072EE000200 0
073 A010200 0.0000
073 A020200 0.0000
073 B000200 0.0000
073 C000200 0.0000
074 A000200 0
074 B000200 0
074 C000200 177650
074 D000200 0
074 E000200 0
074 F000200 0
074 G000200 0
074 H000200 0
074 I000200 0
074 J000200 0
074 K000200 0
074 L000200 1743
074 M000200 9
074 N000200 179402
074 O000200 0
074 P000200 23
074 Q000200 0
074 R010200 0
074 R020200 0
074 R030200 0
074 R040200 50
074 S000200 0
074 T000200 179329
074 U010200 0
074 U020200 0
074 V010200 0.00
074 V020200 0.00
074 W000200 0.0000
074 X000200 1
074 Y000200 0
075 A000200 177801
075 B000200 0
076 000200 0.00
008 A000301 INVESTORS BANK & TRUST COMPNAY
008 B000301 A
008 C000301 801-n/a
008 D010301 BOSTON
008 D020301 MA
008 D030301 02116
008 A000302 M & I INVESTMENT MANAGEMENT CORP.
008 B000302 S
008 C000302 801-9118
008 D010302 MIWAUKEE
008 D020302 WI
008 D030302 53202
024 000300 N
<PAGE> PAGE 13
028 A010300 78908
028 A020300 0
028 A030300 0
028 A040300 87971
028 B010300 88630
028 B020300 0
028 B030300 0
028 B040300 48616
028 C010300 43032
028 C020300 0
028 C030300 0
028 C040300 67822
028 D010300 76344
028 D020300 0
028 D030300 0
028 D040300 49354
028 E010300 116517
028 E020300 0
028 E030300 0
028 E040300 106540
028 F010300 204022
028 F020300 0
028 F030300 0
028 F040300 201717
028 G010300 607453
028 G020300 0
028 G030300 0
028 G040300 562020
028 H000300 0
062 A000300 Y
062 B000300 27.5
062 C000300 0.0
062 D000300 68.9
062 E000300 0.0
062 F000300 0.0
062 G000300 0.0
062 H000300 0.0
062 I000300 0.0
062 J000300 0.0
062 K000300 0.0
062 L000300 4.2
062 M000300 0.0
062 N000300 0.0
062 O000300 0.0
062 P000300 0.0
062 Q000300 0.0
062 R000300 0.0
063 A000300 8
063 B000300 0.0
064 A000300 N
064 B000300 N
<PAGE> PAGE 14
070 A010300 Y
070 A020300 Y
070 B010300 N
070 B020300 N
070 C010300 N
070 C020300 N
070 D010300 N
070 D020300 N
070 E010300 N
070 E020300 N
070 F010300 N
070 F020300 N
070 G010300 N
070 G020300 N
070 H010300 N
070 H020300 N
070 I010300 N
070 I020300 N
070 J010300 Y
070 J020300 N
070 K010300 Y
070 K020300 Y
070 L010300 N
070 L020300 N
070 M010300 N
070 M020300 N
070 N010300 Y
070 N020300 N
070 O010300 Y
070 O020300 N
070 P010300 N
070 P020300 N
070 Q010300 N
070 Q020300 N
070 R010300 N
070 R020300 N
071 A000300 0
071 B000300 0
071 C000300 0
071 D000300 0
072 A000300 12
072 B000300 11648
072 C000300 3
072 D000300 0
072 E000300 0
072 F000300 398
072 G000300 0
072 H000300 0
072 I000300 0
072 J000300 0
072 K000300 0
<PAGE> PAGE 15
072 L000300 0
072 M000300 14
072 N000300 0
072 O000300 0
072 P000300 0
072 Q000300 0
072 R000300 23
072 S000300 19
072 T000300 0
072 U000300 0
072 V000300 0
072 W000300 40
072 X000300 494
072 Y000300 0
072 Z000300 11157
072AA000300 0
072BB000300 0
072CC010300 0
072CC020300 0
072DD010300 0
072DD020300 0
072EE000300 0
073 A010300 0.0000
073 A020300 0.0000
073 B000300 0.0000
073 C000300 0.0000
074 A000300 0
074 B000300 193128
074 C000300 89763
074 D000300 0
074 E000300 0
074 F000300 0
074 G000300 0
074 H000300 0
074 I000300 0
074 J000300 0
074 K000300 0
074 L000300 19
074 M000300 10
074 N000300 282920
074 O000300 0
074 P000300 35
074 Q000300 0
074 R010300 0
074 R020300 0
074 R030300 0
074 R040300 40
074 S000300 0
074 T000300 282845
074 U010300 0
074 U020300 0
<PAGE> PAGE 16
074 V010300 0.00
074 V020300 0.00
074 W000300 0.0000
074 X000300 1
074 Y000300 0
075 A000300 248239
075 B000300 0
076 000300 0.00
008 A000401 INVESTORS BANK & TRUST COMPANY
008 B000401 A
008 C000401 801-n/a
008 D010401 BOSTON
008 D020401 MA
008 D030401 02116
008 A000402 ALLMERICA ASSET MANAGEMENT, INC.
008 B000402 S
008 C000402 801-44189
008 D010402 WORCESTER
008 D020402 MA
008 D030402 01653
024 000400 N
028 A010400 80853
028 A020400 0
028 A030400 0
028 A040400 95448
028 B010400 65473
028 B020400 0
028 B030400 0
028 B040400 72892
028 C010400 83556
028 C020400 0
028 C030400 0
028 C040400 75065
028 D010400 101827
028 D020400 0
028 D030400 0
028 D040400 126366
028 E010400 52680
028 E020400 0
028 E030400 0
028 E040400 72769
028 F010400 143660
028 F020400 0
028 F030400 0
028 F040400 127300
028 G010400 528049
028 G020400 0
028 G030400 0
028 G040400 569840
028 H000400 0
062 A000400 Y
<PAGE> PAGE 17
062 B000400 0.0
062 C000400 91.9
062 D000400 0.0
062 E000400 0.0
062 F000400 0.0
062 G000400 0.0
062 H000400 0.0
062 I000400 0.0
062 J000400 0.0
062 K000400 0.0
062 L000400 6.8
062 M000400 0.0
062 N000400 0.0
062 O000400 0.0
062 P000400 0.0
062 Q000400 0.0
062 R000400 0.0
063 A000400 66
063 B000400 0.0
064 A000400 N
064 B000400 N
070 A010400 Y
070 A020400 N
070 B010400 N
070 B020400 N
070 C010400 N
070 C020400 N
070 D010400 N
070 D020400 N
070 E010400 N
070 E020400 N
070 F010400 N
070 F020400 N
070 G010400 N
070 G020400 N
070 H010400 N
070 H020400 N
070 I010400 N
070 I020400 N
070 J010400 Y
070 J020400 N
070 K010400 Y
070 K020400 Y
070 L010400 N
070 L020400 N
070 M010400 N
070 M020400 N
070 N010400 Y
070 N020400 N
070 O010400 Y
070 O020400 N
<PAGE> PAGE 18
070 P010400 N
070 P020400 N
070 Q010400 N
070 Q020400 N
070 R010400 N
070 R020400 N
071 A000400 0
071 B000400 0
071 C000400 0
071 D000400 0
072 A000400 7
072 B000400 3865
072 C000400 35
072 D000400 0
072 E000400 0
072 F000400 123
072 G000400 0
072 H000400 0
072 I000400 0
072 J000400 0
072 K000400 0
072 L000400 0
072 M000400 2
072 N000400 0
072 O000400 0
072 P000400 0
072 Q000400 0
072 R000400 15
072 S000400 6
072 T000400 0
072 U000400 0
072 V000400 0
072 W000400 16
072 X000400 162
072 Y000400 0
072 Z000400 3739
072AA000400 1
072BB000400 0
072CC010400 0
072CC020400 0
072DD010400 0
072DD020400 0
072EE000400 0
073 A010400 0.0000
073 A020400 0.0000
073 B000400 0.0000
073 C000400 0.0000
074 A000400 710
074 B000400 0
074 C000400 129553
074 D000400 0
<PAGE> PAGE 19
074 E000400 0
074 F000400 0
074 G000400 0
074 H000400 0
074 I000400 0
074 J000400 0
074 K000400 0
074 L000400 1089
074 M000400 3
074 N000400 131355
074 O000400 0
074 P000400 17
074 Q000400 0
074 R010400 0
074 R020400 0
074 R030400 0
074 R040400 20
074 S000400 0
074 T000400 131318
074 U010400 0
074 U020400 0
074 V010400 0.00
074 V020400 0.00
074 W000400 0.0000
074 X000400 1
074 Y000400 0
075 A000400 142454
075 B000400 0
076 000400 0.00
SIGNATURE PAUL JASINSKI
TITLE TREASURER
<TABLE> <S> <C>
<ARTICLE> 6
<LEGEND>
This schedule contains summary financial information
extracted from The Merrimac Cash Portfolio
form N-SAR for the period ended December 31, 1999
and is qualified in its entirety by reference to
such financial statements.
</LEGEND>
<SERIES>
<NUMBER> 1
<NAME> Merrimac Cash Portfolio
<S> <C>
<PERIOD-TYPE> 12-MOS
<FISCAL-YEAR-END> DEC-31-1999
<PERIOD-END> DEC-31-1999
<INVESTMENTS-AT-COST> 1,131,625,345
<INVESTMENTS-AT-VALUE> 1,131,625,345
<RECEIVABLES> 9,575,199
<ASSETS-OTHER> 620,501
<OTHER-ITEMS-ASSETS> 22,902
<TOTAL-ASSETS> 1,141,843,947
<PAYABLE-FOR-SECURITIES> 60,132,146
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 218,492
<TOTAL-LIABILITIES> 60,350,638
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1,081,493,309
<SHARES-COMMON-STOCK> 0
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 1,081,493,309
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 66,351,698
<OTHER-INCOME> 0
<EXPENSES-NET> 2,397,639
<NET-INVESTMENT-INCOME> 63,954,059
<REALIZED-GAINS-CURRENT> (144,611)
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 63,809,448
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 6,036,333,627
<NUMBER-OF-SHARES-REDEEMED> 5,811,849,613
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 288,293,462
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 2,117,982
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 2,397,639
<AVERAGE-NET-ASSETS> 1,245,261,429
<PER-SHARE-NAV-BEGIN> 0.00
<PER-SHARE-NII> 0.00
<PER-SHARE-GAIN-APPREC> 0.00
<PER-SHARE-DIVIDEND> 0.00
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 0.00
<EXPENSE-RATIO> 0.19
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<LEGEND>
This schedule contains summary financial information
extracted from The Merrimac Treasury Portfolio
form N-SAR for the period ended December 31, 1999
and is qualified in its entirety by reference to
such financial statements.
</LEGEND>
<SERIES>
<NUMBER> 2
<NAME> Merrimac Treasury Portfolio
<S> <C>
<PERIOD-TYPE> 12-MOS
<FISCAL-YEAR-END> DEC-31-1999
<PERIOD-END> DEC-31-1999
<INVESTMENTS-AT-COST> 177,649,582
<INVESTMENTS-AT-VALUE> 177,649,582
<RECEIVABLES> 1,742,976
<ASSETS-OTHER> 6,731
<OTHER-ITEMS-ASSETS> 3,209
<TOTAL-ASSETS> 179,402,498
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 73,575
<TOTAL-LIABILITIES> 73,575
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 179,328,923
<SHARES-COMMON-STOCK> 0
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 179,328,923
<DIVIDEND-INCOME> 443,188
<INTEREST-INCOME> 7,916,343
<OTHER-INCOME> 0
<EXPENSES-NET> 381,319
<NET-INVESTMENT-INCOME> 7,978,212
<REALIZED-GAINS-CURRENT> (3,632)
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 7,974,580
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 695,212,525
<NUMBER-OF-SHARES-REDEEMED> 638,584,123
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 64,602,982
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 302,524
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 381,319
<AVERAGE-NET-ASSETS> 177,800,655
<PER-SHARE-NAV-BEGIN> 0.00
<PER-SHARE-NII> 0.00
<PER-SHARE-GAIN-APPREC> 0.00
<PER-SHARE-DIVIDEND> 0.00
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 0.00
<EXPENSE-RATIO> 0.21
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<LEGEND>
This schedule contains summary financial information
extracted from The Merrimac Treasury Plus Portfolio
form N-SAR for the period ended December 31, 1999
and is qualified in its entirety by reference to
such financial statements.
</LEGEND>
<SERIES>
<NUMBER> 3
<NAME> Merrimac Treasury Plus Portfolio
<S> <C>
<PERIOD-TYPE> 12-MOS
<FISCAL-YEAR-END> DEC-31-1999
<PERIOD-END> DEC-31-1999
<INVESTMENTS-AT-COST> 282,890,673
<INVESTMENTS-AT-VALUE> 282,890,673
<RECEIVABLES> 19,061
<ASSETS-OTHER> 10,090
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 282,919,824
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 72,226
<TOTAL-LIABILITIES> 72,226
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 282,844,598
<SHARES-COMMON-STOCK> 0
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 282,844,598
<DIVIDEND-INCOME> 3,384
<INTEREST-INCOME> 11,647,269
<OTHER-INCOME> 0
<EXPENSES-NET> 493,875
<NET-INVESTMENT-INCOME> 11,156,778
<REALIZED-GAINS-CURRENT> (66)
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 11,156,712
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 1,227,975,120
<NUMBER-OF-SHARES-REDEEMED> 956,287,234
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 282,844,598
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 397,835
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 493,875
<AVERAGE-NET-ASSETS> 248,239,497
<PER-SHARE-NAV-BEGIN> 0.00
<PER-SHARE-NII> 0.00
<PER-SHARE-GAIN-APPREC> 0.00
<PER-SHARE-DIVIDEND> 0.00
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 0.00
<EXPENSE-RATIO> 0.21
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<LEGEND>
This schedule contains summary financial information
extracted from The Merrimac U.S. Government Portfolio
form N-SAR for the period ended December 31, 1999
and is qualified in its entirety by reference to
such financial statements.
</LEGEND>
<SERIES>
<NUMBER> 4
<NAME> Merrimac U.S. Government Portfolio
<S> <C>
<PERIOD-TYPE> 12-MOS
<FISCAL-YEAR-END> DEC-31-1999
<PERIOD-END> DEC-31-1999
<INVESTMENTS-AT-COST> 129,552,921
<INVESTMENTS-AT-VALUE> 129,552,921
<RECEIVABLES> 1,089,444
<ASSETS-OTHER> 713,054
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 131,355,419
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 37,146
<TOTAL-LIABILITIES> 37,146
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 131,318,273
<SHARES-COMMON-STOCK> 0
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 131,318,273
<DIVIDEND-INCOME> 35,499
<INTEREST-INCOME> 3,864,900
<OTHER-INCOME> 0
<EXPENSES-NET> 161,718
<NET-INVESTMENT-INCOME> 3,738,681
<REALIZED-GAINS-CURRENT> 1,006
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 3,739,687
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 697,418,162
<NUMBER-OF-SHARES-REDEEMED> 569,839,576
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 131,318,273
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 123,332
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 161,718
<AVERAGE-NET-ASSETS> 142,454,452
<PER-SHARE-NAV-BEGIN> 0.00
<PER-SHARE-NII> 0.00
<PER-SHARE-GAIN-APPREC> 0.00
<PER-SHARE-DIVIDEND> 0.00
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 0.00
<EXPENSE-RATIO> 0.22
</TABLE>
Report of Independent Auditors
To the Board of Trustees and
Owners of Beneficial Interest of
Merrimac Master Portfolio
In planning and performing our audit of the financial statements of the Merrimac
Cash Portfolio, the Merrimac Treasury Portfolio, the Merrimac Treasury Plus
Portfolio, and the Merrimac U.S. Government Portfolio (collectively, the
"Portfolios"), four of the series comprising the Merrimac Master Portfolio (the
"Portfolio Trust"), 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 the Portfolio Trust 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 at
December 31, 1999.
This report is intended solely for the information and use of management, the
Board of Trustees of the Portfolio Trust, and the Securities and Exchange
Commission and is not intended to be and should not be used by anyone other than
these specified parties.
February 11, 2000
