<PAGE> PAGE 1
000 B000000 09/30/1999
000 C000000 0000356682
000 D000000 N
000 E000000 NF
000 F000000 Y
000 G000000 N
000 H000000 N
000 I000000 6.1
000 J000000 A
001 A000000 CALVERT SOCIAL INVESTMENT FUND
001 B000000 811-3334
001 C000000 3019514881
002 A000000 4550 MONTGOMERY AVE., SUITE 1000N
002 B000000 BETHESDA
002 C000000 MD
002 D010000 20814
003 000000 N
004 000000 N
005 000000 N
006 000000 N
007 A000000 Y
007 B000000 5
007 C010100 1
007 C020100 MONEY MARKET PORTFOLIO
007 C030100 N
007 C010200 2
007 C020200 MANAGED GROWTH PORTFOLIO
007 C030200 N
007 C010300 3
007 C020300 BOND PORTFOLIO
007 C030300 N
007 C010400 4
007 C020400 EQUITY PORTFOLIO
007 C030400 N
007 C010500 5
007 C020500 MANAGED INDEX PORTFOLIO
007 C030500 N
007 C010600 6
007 C010700 7
007 C010800 8
007 C010900 9
007 C011000 10
020 A000001 BOSTON INSTITUTIIONAL SERVICES
020 C000001 119
020 A000002 AUTRANET INC
020 C000002 56
020 A000003 DONALDSON LUFKIN & JENRETTE SECS
020 C000003 36
020 A000004 PERSHING DIVISION OF DONALDSON LUFTKIN
020 C000004 35
020 A000005 JEFFERIES & CO
<PAGE> PAGE 2
020 C000005 25
020 A000006 BUCKINGHAM RESEARCH GROUP
020 C000006 24
020 A000007 CANTOR FITZGERALD & CO INC
020 C000007 23
020 A000008 GOLDMAN SACHS & CO
020 C000008 22
020 A000009 MORGAN STANLEY AND CO INC
020 C000009 21
020 A000010 BERNSTEIN SANFORD C & CO INC
020 C000010 21
021 000000 788
022 A000001 STATE STREET BANK & TRUST CO DEALER DEPT
022 C000001 4487594
022 D000001 0
022 A000002 DONALDSON LUFKIN & JENRETTE SECS
022 C000002 4349542
022 D000002 108199
022 A000003 GOLDMAN SACKS & CO
022 C000003 155365
022 D000003 109237
022 A000004 SALOMON SMITH BARNEY INC
022 C000004 148833
022 D000004 195472
022 A000005 M L PIERCE FENNER SMITH INC FIXED OPER
022 C000005 202150
022 D000005 127596
022 A000006 CHASE SECURITIES
022 C000006 171268
022 D000006 145634
022 A000007 LEHMAN BORS INC
022 C000007 105909
022 D000007 73992
022 A000008 PAINE WEBBER INCORPORATED
022 C000008 103731
022 D000008 12343
022 A000009 ABN AMRO BOND TRADING
022 C000009 55301
022 D000009 52632
022 A000010 DEUTSCHE BANK AG
022 C000010 63548
022 D000010 74541
023 C000000 9843241
023 D000000 899646
027 000000 Y
077 A000000 Y
077 B000000 Y
080 C00AA00 8000
081 A00AA00 Y
081 B00AA00 37
082 A00AA00 N
<PAGE> PAGE 3
082 B00AA00 0
083 A00AA00 N
083 B00AA00 0
084 A00AA00 N
084 B00AA00 0
085 A00AA00 Y
085 B00AA00 N
028 A010100 20186
028 A020100 634
028 A030100 0
028 A040100 -21693
028 B010100 12476
028 B020100 568
028 B030100 0
028 B040100 -16193
028 C010100 19501
028 C020100 677
028 C030100 0
028 C040100 -15181
028 D010100 13348
028 D020100 642
028 D030100 0
028 D040100 -17425
028 E010100 12693
028 E020100 688
028 E030100 0
028 E040100 -15649
028 F010100 22727
028 F020100 667
028 F030100 0
028 F040100 -19005
028 G010100 100931
028 G020100 3876
028 G030100 0
028 G040100 -105146
028 H000100 0
029 000100 N
030 A000100 0
030 B000100 0.00
030 C000100 0.00
062 A000100 Y
062 B000100 0.0
062 C000100 19.4
062 D000100 3.3
062 E000100 0.0
062 F000100 2.2
062 G000100 0.0
062 H000100 0.0
062 I000100 3.0
062 J000100 71.7
062 K000100 0.0
<PAGE> PAGE 4
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 46
063 B000100 0.0
071 A000100 0
071 B000100 0
071 C000100 0
071 D000100 0
072 A000100 6
072 B000100 9967
072 C000100 0
072 D000100 0
072 E000100 0
072 F000100 713
072 G000100 227
072 H000100 0
072 I000100 490
072 J000100 34
072 K000100 26
072 L000100 54
072 M000100 40
072 N000100 33
072 O000100 0
072 P000100 0
072 Q000100 0
072 R000100 9
072 S000100 14
072 T000100 0
072 U000100 0
072 V000100 0
072 W000100 51
072 X000100 1690
072 Y000100 49
072 Z000100 8326
072AA000100 0
072BB000100 69
072CC010100 0
072CC020100 0
072DD010100 8337
072DD020100 0
072EE000100 0
073 A010100 0.0445
073 A020100 0.0000
073 B000100 0.0000
073 C000100 0.0000
074 A000100 375
<PAGE> PAGE 5
074 B000100 6400
074 C000100 186713
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 2562
074 M000100 15
074 N000100 196066
074 O000100 0
074 P000100 147
074 Q000100 0
074 R010100 0
074 R020100 0
074 R030100 0
074 R040100 1978
074 S000100 0
074 T000100 193941
074 U010100 194031
074 U020100 0
074 V010100 1.00
074 V020100 0.00
074 W000100 0.0000
074 X000100 11591
074 Y000100 0
075 A000100 187937
075 B000100 0
076 000100 0.00
028 A010200 21303
028 A020200 0
028 A030200 0
028 A040200 -22255
028 B010200 7161
028 B020200 0
028 B030200 0
028 B040200 -6956
028 C010200 5350
028 C020200 3254
028 C030200 0
028 C040200 -6136
028 D010200 6430
028 D020200 0
028 D030200 0
028 D040200 -8294
028 E010200 4508
028 E020200 0
028 E030200 0
<PAGE> PAGE 6
028 E040200 -7446
028 F010200 4426
028 F020200 3543
028 F030200 0
028 F040200 -7437
028 G010200 49178
028 G020200 6797
028 G030200 0
028 G040200 -58524
028 H000200 30278
029 000200 Y
030 A000200 508
030 B000200 4.75
030 C000200 0.00
031 A000200 117
031 B000200 0
032 000200 337
033 000200 54
042 A000200 25
042 B000200 10
042 C000200 7
042 D000200 53
042 E000200 5
042 F000200 5
042 G000200 0
042 H000200 0
043 000200 1745
044 000200 0
062 A000200 Y
062 B000200 0.0
062 C000200 0.0
062 D000200 0.0
062 E000200 0.0
062 F000200 0.1
062 G000200 0.0
062 H000200 0.0
062 I000200 2.0
062 J000200 0.0
062 K000200 0.0
062 L000200 0.0
062 M000200 0.0
062 N000200 0.0
062 O000200 5.5
062 P000200 37.0
062 Q000200 0.6
062 R000200 55.7
063 A000200 0
063 B000200 13.0
071 A000200 559742
071 B000200 565068
071 C000200 715986
<PAGE> PAGE 7
071 D000200 78
072 A000200 6
072 B000200 20767
072 C000200 3410
072 D000200 0
072 E000200 0
072 F000200 3810
072 G000200 1247
072 H000200 0
072 I000200 1212
072 J000200 124
072 K000200 79
072 L000200 92
072 M000200 143
072 N000200 82
072 O000200 0
072 P000200 0
072 Q000200 0
072 R000200 36
072 S000200 66
072 T000200 1944
072 U000200 0
072 V000200 0
072 W000200 150
072 X000200 8982
072 Y000200 105
072 Z000200 15299
072AA000200 43854
072BB000200 0
072CC010200 68248
072CC020200 0
072DD010200 14416
072DD020200 73
072EE000200 71195
073 A010200 0.6675
073 A020200 0.3405
073 B000200 3.3605
073 C000200 0.0000
074 A000200 613
074 B000200 0
074 C000200 829
074 D000200 336354
074 E000200 0
074 F000200 411981
074 G000200 0
074 H000200 0
074 I000200 3393
074 J000200 24413
074 K000200 0
074 L000200 5809
074 M000200 97
<PAGE> PAGE 8
074 N000200 783490
074 O000200 36340
074 P000200 743
074 Q000200 0
074 R010200 0
074 R020200 0
074 R030200 0
074 R040200 738
074 S000200 0
074 T000200 745669
074 U010200 22049
074 U020200 310
074 V010200 32.14
074 V020200 31.97
074 W000200 0.0000
074 X000200 36783
074 Y000200 0
075 A000200 0
075 B000200 754095
076 000200 0.00
028 A010300 1739
028 A020300 259
028 A030300 0
028 A040300 -3947
028 B010300 1395
028 B020300 292
028 B030300 0
028 B040300 -1217
028 C010300 1521
028 C020300 261
028 C030300 0
028 C040300 -1075
028 D010300 1603
028 D020300 277
028 D030300 0
028 D040300 -1450
028 E010300 1870
028 E020300 276
028 E030300 0
028 E040300 -1002
028 F010300 2203
028 F020300 288
028 F030300 0
028 F040300 -2088
028 G010300 10331
028 G020300 1653
028 G030300 0
028 G040300 -10779
028 H000300 8849
029 000300 Y
030 A000300 113
<PAGE> PAGE 9
030 B000300 3.75
030 C000300 0.00
031 A000300 31
031 B000300 0
032 000300 70
033 000300 12
042 A000300 19
042 B000300 6
042 C000300 5
042 D000300 55
042 E000300 15
042 F000300 0
042 G000300 0
042 H000300 0
043 000300 350
044 000300 0
062 A000300 Y
062 B000300 0.0
062 C000300 3.9
062 D000300 6.0
062 E000300 0.0
062 F000300 0.1
062 G000300 0.0
062 H000300 0.0
062 I000300 0.0
062 J000300 0.0
062 K000300 0.0
062 L000300 0.0
062 M000300 0.0
062 N000300 0.0
062 O000300 2.1
062 P000300 90.6
062 Q000300 0.6
062 R000300 1.5
063 A000300 0
063 B000300 17.0
071 A000300 156160
071 B000300 148557
071 C000300 66205
071 D000300 224
072 A000300 6
072 B000300 4746
072 C000300 56
072 D000300 0
072 E000300 0
072 F000300 301
072 G000300 84
072 H000300 0
072 I000300 162
072 J000300 34
072 K000300 8
<PAGE> PAGE 10
072 L000300 10
072 M000300 15
072 N000300 41
072 O000300 0
072 P000300 0
072 Q000300 0
072 R000300 4
072 S000300 5
072 T000300 164
072 U000300 0
072 V000300 0
072 W000300 13
072 X000300 842
072 Y000300 40
072 Z000300 4001
072AA000300 0
072BB000300 1435
072CC010300 0
072CC020300 1518
072DD010300 3858
072DD020300 83
072EE000300 3364
073 A010300 0.9272
073 A020300 0.7130
073 B000300 0.5467
073 C000300 0.0000
074 A000300 253
074 B000300 4300
074 C000300 100
074 D000300 69487
074 E000300 0
074 F000300 1051
074 G000300 0
074 H000300 0
074 I000300 0
074 J000300 8475
074 K000300 0
074 L000300 1074
074 M000300 23
074 N000300 84763
074 O000300 13108
074 P000300 72
074 Q000300 0
074 R010300 0
074 R020300 0
074 R030300 0
074 R040300 87
074 S000300 0
074 T000300 71496
074 U010300 4295
074 U020300 178
<PAGE> PAGE 11
074 V010300 15.59
074 V020300 15.53
074 W000300 0.0000
074 X000300 4923
074 Y000300 0
075 A000300 0
075 B000300 69860
076 000300 0.00
028 A010400 4571
028 A020400 0
028 A030400 0
028 A040400 -3447
028 B010400 3000
028 B020400 0
028 B030400 0
028 B040400 -2763
028 C010400 3747
028 C020400 0
028 C030400 0
028 C040400 -1868
028 D010400 5070
028 D020400 0
028 D030400 0
028 D040400 -2911
028 E010400 5003
028 E020400 0
028 E030400 0
028 E040400 -2791
028 F010400 7525
028 F020400 0
028 F030400 0
028 F040400 -4340
028 G010400 28916
028 G020400 0
028 G030400 0
028 G040400 -18120
028 H000400 20923
029 000400 Y
030 A000400 392
030 B000400 4.75
030 C000400 0.00
031 A000400 87
031 B000400 0
032 000400 280
033 000400 25
042 A000400 17
042 B000400 8
042 C000400 5
042 D000400 60
042 E000400 9
042 F000400 0
<PAGE> PAGE 12
042 G000400 0
042 H000400 0
043 000400 373
044 000400 0
062 A000400 N
062 B000400 0.0
062 C000400 0.0
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 0.0
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 0
063 B000400 0.0
071 A000400 44728
071 B000400 50198
071 C000400 153304
071 D000400 29
072 A000400 6
072 B000400 79
072 C000400 1304
072 D000400 0
072 E000400 51
072 F000400 897
072 G000400 224
072 H000400 0
072 I000400 437
072 J000400 24
072 K000400 28
072 L000400 31
072 M000400 37
072 N000400 41
072 O000400 0
072 P000400 0
072 Q000400 0
072 R000400 8
072 S000400 13
072 T000400 503
072 U000400 0
072 V000400 0
072 W000400 38
<PAGE> PAGE 13
072 X000400 2281
072 Y000400 228
072 Z000400 -618
072AA000400 10181
072BB000400 0
072CC010400 32844
072CC020400 0
072DD010400 0
072DD020400 0
072EE000400 89
073 A010400 0.0000
073 A020400 0.0000
073 B000400 0.0141
073 C000400 0.0000
074 A000400 346
074 B000400 7000
074 C000400 0
074 D000400 1347
074 E000400 0
074 F000400 175341
074 G000400 0
074 H000400 0
074 I000400 0
074 J000400 467
074 K000400 0
074 L000400 934
074 M000400 18
074 N000400 185452
074 O000400 0
074 P000400 202
074 Q000400 0
074 R010400 0
074 R020400 0
074 R030400 0
074 R040400 83
074 S000400 0
074 T000400 185167
074 U010400 6160
074 U020400 302
074 V010400 27.06
074 V020400 26.60
074 W000400 0.0000
074 X000400 15333
074 Y000400 0
075 A000400 0
075 B000400 175201
076 000400 0.00
028 A010500 2318
028 A020500 0
028 A030500 0
028 A040500 -175
<PAGE> PAGE 14
028 B010500 873
028 B020500 0
028 B030500 0
028 B040500 -103
028 C010500 1056
028 C020500 0
028 C030500 0
028 C040500 -523
028 D010500 1192
028 D020500 0
028 D030500 0
028 D040500 -385
028 E010500 1077
028 E020500 0
028 E030500 0
028 E040500 -154
028 F010500 725
028 F020500 0
028 F030500 0
028 F040500 -194
028 G010500 7241
028 G020500 0
028 G030500 0
028 G040500 -1534
028 H000500 4242
029 000500 Y
030 A000500 90
030 B000500 0.00
030 C000500 0.00
031 A000500 20
031 B000500 0
032 000500 64
033 000500 6
042 A000500 31
042 B000500 18
042 C000500 3
042 D000500 29
042 E000500 19
042 F000500 0
042 G000500 0
042 H000500 0
043 000500 23
044 000500 0
062 A000500 N
062 B000500 0.0
062 C000500 0.0
062 D000500 0.0
062 E000500 0.0
062 F000500 0.0
062 G000500 0.0
062 H000500 0.0
<PAGE> PAGE 15
062 I000500 0.0
062 J000500 0.0
062 K000500 0.0
062 L000500 0.0
062 M000500 0.0
062 N000500 0.0
062 O000500 0.0
062 P000500 0.0
062 Q000500 0.0
062 R000500 0.0
063 A000500 0
063 B000500 0.0
071 A000500 17768
071 B000500 11477
071 C000500 26330
071 D000500 44
072 A000500 6
072 B000500 0
072 C000500 441
072 D000500 0
072 E000500 0
072 F000500 190
072 G000500 38
072 H000500 0
072 I000500 47
072 J000500 31
072 K000500 0
072 L000500 2
072 M000500 8
072 N000500 40
072 O000500 0
072 P000500 0
072 Q000500 0
072 R000500 -4
072 S000500 2
072 T000500 65
072 U000500 0
072 V000500 0
072 W000500 3
072 X000500 424
072 Y000500 68
072 Z000500 85
072AA000500 0
072BB000500 534
072CC010500 3523
072CC020500 0
072DD010500 20
072DD020500 0
072EE000500 0
073 A010500 0.0491
073 A020500 0.0000
<PAGE> PAGE 16
073 B000500 0.0000
073 C000500 0.0000
074 A000500 581
074 B000500 0
074 C000500 0
074 D000500 0
074 E000500 0
074 F000500 37067
074 G000500 0
074 H000500 0
074 I000500 0
074 J000500 81
074 K000500 0
074 L000500 36
074 M000500 9
074 N000500 37773
074 O000500 283
074 P000500 36
074 Q000500 0
074 R010500 0
074 R020500 0
074 R030500 0
074 R040500 15
074 S000500 0
074 T000500 37439
074 U010500 728
074 U020500 246
074 V010500 16.83
074 V020500 16.58
074 W000500 0.0000
074 X000500 1029
074 Y000500 0
075 A000500 31636
075 B000500 0
076 000500 0.00
SIGNATURE WILLIAM M. TARTIKOFF
TITLE GENERAL COUNSEL
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 123
<NAME> MONEY MARKET PORTFOLIO
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 193113
<INVESTMENTS-AT-VALUE> 193113
<RECEIVABLES> 2562
<ASSETS-OTHER> 391
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 196066
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 2125
<TOTAL-LIABILITIES> 2125
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 193988
<SHARES-COMMON-STOCK> 194031
<SHARES-COMMON-PRIOR> 172739
<ACCUMULATED-NII-CURRENT> 1
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (48)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 193941
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 9967
<OTHER-INCOME> 0
<EXPENSES-NET> 1641
<NET-INVESTMENT-INCOME> 8326
<REALIZED-GAINS-CURRENT> (40476)
<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> (32150)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (8337)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 210031
<NUMBER-OF-SHARES-REDEEMED> (196454)
<SHARES-REINVESTED> 7715
<NET-CHANGE-IN-ASSETS> (19195)
<ACCUMULATED-NII-PRIOR> 13
<ACCUMULATED-GAINS-PRIOR> (29)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 713
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 1673
<AVERAGE-NET-ASSETS> 187937
<PER-SHARE-NAV-BEGIN> 1.000
<PER-SHARE-NII> 0.044
<PER-SHARE-GAIN-APPREC> 0.00
<PER-SHARE-DIVIDEND> (0.044)
<PER-SHARE-DISTRIBUTIONS> 0.0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.000
<EXPENSE-RATIO> 0.87
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 124
<NAME> BALANCED PORTFOLIO, CLASS A
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 684306
<INVESTMENTS-AT-VALUE> 752558
<RECEIVABLES> 30222
<ASSETS-OTHER> 710
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 783490
<PAYABLE-FOR-SECURITIES> 36340
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 1481
<TOTAL-LIABILITIES> 37821
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 594238
<SHARES-COMMON-STOCK> 22049
<SHARES-COMMON-PRIOR> 20768
<ACCUMULATED-NII-CURRENT> 1505
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 43377
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 69535
<NET-ASSETS> 708655
<DIVIDEND-INCOME> 3291
<INTEREST-INCOME> 20053
<OTHER-INCOME> 0
<EXPENSES-NET> 8389
<NET-INVESTMENT-INCOME> 14955
<REALIZED-GAINS-CURRENT> 43959
<APPREC-INCREASE-CURRENT> 19619
<NET-CHANGE-FROM-OPS> 78533
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (14416)
<DISTRIBUTIONS-OF-GAINS> (69564)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 91354
<NUMBER-OF-SHARES-REDEEMED> (128869)
<SHARES-REINVESTED> 77715
<NET-CHANGE-IN-ASSETS> 34753
<ACCUMULATED-NII-PRIOR> 971
<ACCUMULATED-GAINS-PRIOR> 68983
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 3686
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 8490
<AVERAGE-NET-ASSETS> 728159
<PER-SHARE-NAV-BEGIN> 32.450
<PER-SHARE-NII> 0.680
<PER-SHARE-GAIN-APPREC> 3.032
<PER-SHARE-DIVIDEND> (0.661)
<PER-SHARE-DISTRIBUTIONS> (3.361)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 32.140
<EXPENSE-RATIO> 1.15
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 125
<NAME> BALANCED PORTFOLIO, CLASS B
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 666772
<INVESTMENTS-AT-VALUE> 752558
<RECEIVABLES> 30222
<ASSETS-OTHER> 710
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 783490
<PAYABLE-FOR-SECURITIES> 36340
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 1481
<TOTAL-LIABILITIES> 37821
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 10297
<SHARES-COMMON-STOCK> 310
<SHARES-COMMON-PRIOR> 78
<ACCUMULATED-NII-CURRENT> (25)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (48)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (314)
<NET-ASSETS> 9910
<DIVIDEND-INCOME> 29
<INTEREST-INCOME> 60
<OTHER-INCOME> 0
<EXPENSES-NET> 155
<NET-INVESTMENT-INCOME> (66)
<REALIZED-GAINS-CURRENT> 339
<APPREC-INCREASE-CURRENT> (176)
<NET-CHANGE-FROM-OPS> 97
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (73)
<DISTRIBUTIONS-OF-GAINS> (412)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 7832
<NUMBER-OF-SHARES-REDEEMED> (638)
<SHARES-REINVESTED> 442
<NET-CHANGE-IN-ASSETS> 7248
<ACCUMULATED-NII-PRIOR> (7)
<ACCUMULATED-GAINS-PRIOR> 24
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 31
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 157
<AVERAGE-NET-ASSETS> 6533
<PER-SHARE-NAV-BEGIN> 32.380
<PER-SHARE-NII> 0.350
<PER-SHARE-GAIN-APPREC> 2.941
<PER-SHARE-DIVIDEND> (0.341)
<PER-SHARE-DISTRIBUTIONS> (3.361)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 31.970
<EXPENSE-RATIO> 2.38
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 132
<NAME> BALANCED PORTFOLIO, CLASS C
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 666772
<INVESTMENTS-AT-VALUE> 752558
<RECEIVABLES> 30222
<ASSETS-OTHER> 710
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 783490
<PAYABLE-FOR-SECURITIES> 36340
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 1481
<TOTAL-LIABILITIES> 37821
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 13342
<SHARES-COMMON-STOCK> 430
<SHARES-COMMON-PRIOR> 358
<ACCUMULATED-NII-CURRENT> (32)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 312
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 24
<NET-ASSETS> 13646
<DIVIDEND-INCOME> 60
<INTEREST-INCOME> 171
<OTHER-INCOME> 0
<EXPENSES-NET> 289
<NET-INVESTMENT-INCOME> (58)
<REALIZED-GAINS-CURRENT> 798
<APPREC-INCREASE-CURRENT> 248
<NET-CHANGE-FROM-OPS> 989
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (132)
<DISTRIBUTIONS-OF-GAINS> (1219)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 3840
<NUMBER-OF-SHARES-REDEEMED> (2823)
<SHARES-REINVESTED> 1313
<NET-CHANGE-IN-ASSETS> 1968
<ACCUMULATED-NII-PRIOR> (37)
<ACCUMULATED-GAINS-PRIOR> 732
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 67
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 291
<AVERAGE-NET-ASSETS> 13301
<PER-SHARE-NAV-BEGIN> 32.050
<PER-SHARE-NII> 0.360
<PER-SHARE-GAIN-APPREC> 2.981
<PER-SHARE-DIVIDEND> (0.331)
<PER-SHARE-DISTRIBUTIONS> (3.361)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 31.700
<EXPENSE-RATIO> 2.17
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 133
<NAME> BALANCED PORTFOLIO, CLASS I
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 666772
<INVESTMENTS-AT-VALUE> 752558
<RECEIVABLES> 30222
<ASSETS-OTHER> 710
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 783490
<PAYABLE-FOR-SECURITIES> 36340
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 1481
<TOTAL-LIABILITIES> 37821
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 14260
<SHARES-COMMON-STOCK> 419
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> (18)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 213
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (997)
<NET-ASSETS> 13458
<DIVIDEND-INCOME> 6
<INTEREST-INCOME> 3
<OTHER-INCOME> 0
<EXPENSES-NET> 45
<NET-INVESTMENT-INCOME> (36)
<REALIZED-GAINS-CURRENT> 213
<APPREC-INCREASE-CURRENT> (997)
<NET-CHANGE-FROM-OPS> (819)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (173)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 1498
<NUMBER-OF-SHARES-REDEEMED> (872)
<SHARES-REINVESTED> 173
<NET-CHANGE-IN-ASSETS> 13268
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 25
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 45
<AVERAGE-NET-ASSETS> 6102
<PER-SHARE-NAV-BEGIN> 32.520
<PER-SHARE-NII> 0.520
<PER-SHARE-GAIN-APPREC> (0.346)
<PER-SHARE-DIVIDEND> (0.564)
<PER-SHARE-DISTRIBUTIONS> 0.0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 32.130
<EXPENSE-RATIO> 0.73
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 134
<NAME> BOND PORTFOLIO, CLASS A
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 71801
<INVESTMENTS-AT-VALUE> 74938
<RECEIVABLES> 9549
<ASSETS-OTHER> 275
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 84763
<PAYABLE-FOR-SECURITIES> 13108
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 159
<TOTAL-LIABILITIES> 13266
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 69622
<SHARES-COMMON-STOCK> 4295
<SHARES-COMMON-PRIOR> 3897
<ACCUMULATED-NII-CURRENT> 82
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (1310)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (1450)
<NET-ASSETS> 66944
<DIVIDEND-INCOME> 54
<INTEREST-INCOME> 4538
<OTHER-INCOME> 0
<EXPENSES-NET> 725
<NET-INVESTMENT-INCOME> 3867
<REALIZED-GAINS-CURRENT> (1141)
<APPREC-INCREASE-CURRENT> (1941)
<NET-CHANGE-FROM-OPS> 784
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (3858)
<DISTRIBUTIONS-OF-GAINS> (2196)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 18458
<NUMBER-OF-SHARES-REDEEMED> (16967)
<SHARES-REINVESTED> 4916
<NET-CHANGE-IN-ASSETS> 1137
<ACCUMULATED-NII-PRIOR> 73
<ACCUMULATED-GAINS-PRIOR> 2028
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 288
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 758
<AVERAGE-NET-ASSETS> 66829
<PER-SHARE-NAV-BEGIN> 16.880
<PER-SHARE-NII> 0.930
<PER-SHARE-GAIN-APPREC> (0.746)
<PER-SHARE-DIVIDEND> (0.927)
<PER-SHARE-DISTRIBUTIONS> (0.547)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 15.590
<EXPENSE-RATIO> 1.09
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 135
<NAME> BOND PORTFOLIO, CLASS B
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 71801
<INVESTMENTS-AT-VALUE> 74938
<RECEIVABLES> 9549
<ASSETS-OTHER> 275
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 84763
<PAYABLE-FOR-SECURITIES> 13108
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 159
<TOTAL-LIABILITIES> 13266
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 2895
<SHARES-COMMON-STOCK> 178
<SHARES-COMMON-PRIOR> 33
<ACCUMULATED-NII-CURRENT> (4)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (81)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (38)
<NET-ASSETS> 2773
<DIVIDEND-INCOME> 1
<INTEREST-INCOME> 124
<OTHER-INCOME> 0
<EXPENSES-NET> 45
<NET-INVESTMENT-INCOME> 80
<REALIZED-GAINS-CURRENT> (39)
<APPREC-INCREASE-CURRENT> (37)
<NET-CHANGE-FROM-OPS> 4
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (83)
<DISTRIBUTIONS-OF-GAINS> (46)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 2588
<NUMBER-OF-SHARES-REDEEMED> (353)
<SHARES-REINVESTED> 107
<NET-CHANGE-IN-ASSETS> 2215
<ACCUMULATED-NII-PRIOR> (2)
<ACCUMULATED-GAINS-PRIOR> 5
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 8
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 46
<AVERAGE-NET-ASSETS> 1817
<PER-SHARE-NAV-BEGIN> 16.84
<PER-SHARE-NII> 0.74
<PER-SHARE-GAIN-APPREC> (0.790)
<PER-SHARE-DIVIDEND> (0.713)
<PER-SHARE-DISTRIBUTIONS> (0.547)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 15.53
<EXPENSE-RATIO> 2.50
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 136
<NAME> BOND PORTFOLIO, CLASS C
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 71801
<INVESTMENTS-AT-VALUE> 74938
<RECEIVABLES> 9549
<ASSETS-OTHER> 275
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 84763
<PAYABLE-FOR-SECURITIES> 13108
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 159
<TOTAL-LIABILITIES> 13266
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1858
<SHARES-COMMON-STOCK> 115
<SHARES-COMMON-PRIOR> 24
<ACCUMULATED-NII-CURRENT> (5)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (44)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (30)
<NET-ASSETS> 1779
<DIVIDEND-INCOME> 1
<INTEREST-INCOME> 83
<OTHER-INCOME> 0
<EXPENSES-NET> 30
<NET-INVESTMENT-INCOME> 54
<REALIZED-GAINS-CURRENT> (26)
<APPREC-INCREASE-CURRENT> (28)
<NET-CHANGE-FROM-OPS> (1)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (57)
<DISTRIBUTIONS-OF-GAINS> (21)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 4358
<NUMBER-OF-SHARES-REDEEMED> (322)
<SHARES-REINVESTED> 74
<NET-CHANGE-IN-ASSETS> 4031
<ACCUMULATED-NII-PRIOR> (1)
<ACCUMULATED-GAINS-PRIOR> 3
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 5
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 31
<AVERAGE-NET-ASSETS> 1215
<PER-SHARE-NAV-BEGIN> 16.84
<PER-SHARE-NII> 0.74
<PER-SHARE-GAIN-APPREC> (0.807)
<PER-SHARE-DIVIDEND> (0.716)
<PER-SHARE-DISTRIBUTIONS> (0.547)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 15.510
<EXPENSE-RATIO> 2.50
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 141
<NAME> EQUITY PORTFOLIO, CLASS A
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 131235
<INVESTMENTS-AT-VALUE> 183688
<RECEIVABLES> 1401
<ASSETS-OTHER> 363
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 185452
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 285
<TOTAL-LIABILITIES> 285
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 125157
<SHARES-COMMON-STOCK> 6160
<SHARES-COMMON-PRIOR> 6320
<ACCUMULATED-NII-CURRENT> (277)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 10017
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 31819
<NET-ASSETS> 166716
<DIVIDEND-INCOME> 1208
<INTEREST-INCOME> 71
<OTHER-INCOME> 51
<EXPENSES-NET> 1783
<NET-INVESTMENT-INCOME> (453)
<REALIZED-GAINS-CURRENT> 12805
<APPREC-INCREASE-CURRENT> 28760
<NET-CHANGE-FROM-OPS> 41111
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> (83)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 31878
<NUMBER-OF-SHARES-REDEEMED> (34955)
<SHARES-REINVESTED> 81
<NET-CHANGE-IN-ASSETS> 38032
<ACCUMULATED-NII-PRIOR> 175
<ACCUMULATED-GAINS-PRIOR> (2705)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 830
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 1984
<AVERAGE-NET-ASSETS> 162260
<PER-SHARE-NAV-BEGIN> 20.36
<PER-SHARE-NII> (0.07)
<PER-SHARE-GAIN-APPREC> 6.78
<PER-SHARE-DIVIDEND> 0.0
<PER-SHARE-DISTRIBUTIONS> (0.01)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 27.06
<EXPENSE-RATIO> 1.10
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUN
<SERIES>
<NUMBER> 142
<NAME> EQUITY PORTFOLIO, CLASS B
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 131235
<INVESTMENTS-AT-VALUE> 183688
<RECEIVABLES> 1401
<ASSETS-OTHER> 363
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 185452
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 285
<OTHER-ITEMS-LIABILITIES> 0
<TOTAL-LIABILITIES> 285
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 8005
<SHARES-COMMON-STOCK> 302
<SHARES-COMMON-PRIOR> 82
<ACCUMULATED-NII-CURRENT> (72)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 57
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 48
<NET-ASSETS> 8038
<DIVIDEND-INCOME> 35
<INTEREST-INCOME> 2
<OTHER-INCOME> 0
<EXPENSES-NET> 101
<NET-INVESTMENT-INCOME> (64)
<REALIZED-GAINS-CURRENT> 245
<APPREC-INCREASE-CURRENT> 185
<NET-CHANGE-FROM-OPS> 185
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> (2)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 6515
<NUMBER-OF-SHARES-REDEEMED> (512)
<SHARES-REINVESTED> 1
<NET-CHANGE-IN-ASSETS> 6187
<ACCUMULATED-NII-PRIOR> (7)
<ACCUMULATED-GAINS-PRIOR> (185)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 23
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 111
<AVERAGE-NET-ASSETS> 4569
<PER-SHARE-NAV-BEGIN> 20.26
<PER-SHARE-NII> (0.15)
<PER-SHARE-GAIN-APPREC> 6.50
<PER-SHARE-DIVIDEND> 0.0
<PER-SHARE-DISTRIBUTIONS> (0.01)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 26.60
<EXPENSE-RATIO> 2.21
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 144
<NAME> EQUITY PORTFOLIO, CLASS C
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 131235
<INVESTMENTS-AT-VALUE> 183688
<RECEIVABLES> 1401
<ASSETS-OTHER> 363
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 185452
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 285
<TOTAL-LIABILITIES> 285
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 9599
<SHARES-COMMON-STOCK> 417
<SHARES-COMMON-PRIOR> 315
<ACCUMULATED-NII-CURRENT> (269)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 107
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 977
<NET-ASSETS> 10413
<DIVIDEND-INCOME> 62
<INTEREST-INCOME> 5
<OTHER-INCOME> 0
<EXPENSES-NET> 169
<NET-INVESTMENT-INCOME> (102)
<REALIZED-GAINS-CURRENT> 603
<APPREC-INCREASE-CURRENT> 1204
<NET-CHANGE-FROM-OPS> 1705
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> (4)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 4358
<NUMBER-OF-SHARES-REDEEMED> (1630)
<SHARES-REINVESTED> 4
<NET-CHANGE-IN-ASSETS> 4432
<ACCUMULATED-NII-PRIOR> (168)
<ACCUMULATED-GAINS-PRIOR> (492)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 43
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 186
<AVERAGE-NET-ASSETS> 8373
<PER-SHARE-NAV-BEGIN> 19.00
<PER-SHARE-NII> (0.11)
<PER-SHARE-GAIN-APPREC> 6.12
<PER-SHARE-DIVIDEND> 0.0
<PER-SHARE-DISTRIBUTIONS> (0.01)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 25.00
<EXPENSE-RATIO> 2.01
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 145
<NAME> MANAGED INDEX PORTFOLIO, CLASS A
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 33544
<INVESTMENTS-AT-VALUE> 37067
<RECEIVABLES> 117
<ASSETS-OTHER> 590
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 37773
<PAYABLE-FOR-SECURITIES> 283
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 51
<TOTAL-LIABILITIES> 334
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 11499
<SHARES-COMMON-STOCK> 728
<SHARES-COMMON-PRIOR> 325
<ACCUMULATED-NII-CURRENT> (2)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (39)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 799
<NET-ASSETS> 12257
<DIVIDEND-INCOME> 125
<INTEREST-INCOME> 0
<OTHER-INCOME> 0
<EXPENSES-NET> 113
<NET-INVESTMENT-INCOME> 12
<REALIZED-GAINS-CURRENT> (24)
<APPREC-INCREASE-CURRENT> 1200
<NET-CHANGE-FROM-OPS> 1188
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (20)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 8471
<NUMBER-OF-SHARES-REDEEMED> (1803)
<SHARES-REINVESTED> 19
<NET-CHANGE-IN-ASSETS> 7855
<ACCUMULATED-NII-PRIOR> 6
<ACCUMULATED-GAINS-PRIOR> (15)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 45
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 119
<AVERAGE-NET-ASSETS> 9079
<PER-SHARE-NAV-BEGIN> 13.54
<PER-SHARE-NII> 0.03
<PER-SHARE-GAIN-APPREC> 3.31
<PER-SHARE-DIVIDEND> (0.05)
<PER-SHARE-DISTRIBUTIONS> 0.0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 16.83
<EXPENSE-RATIO> 1.25
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 147
<NAME> MANAGED INDEX PORTFOLIO, CLASS B
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 33544
<INVESTMENTS-AT-VALUE> 37067
<RECEIVABLES> 117
<ASSETS-OTHER> 590
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 37773
<PAYABLE-FOR-SECURITIES> 283
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 51
<TOTAL-LIABILITIES> 334
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 3896
<SHARES-COMMON-STOCK> 246
<SHARES-COMMON-PRIOR> 72
<ACCUMULATED-NII-CURRENT> (33)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 15
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 200
<NET-ASSETS> 4078
<DIVIDEND-INCOME> 39
<INTEREST-INCOME> 0
<OTHER-INCOME> 0
<EXPENSES-NET> 70
<NET-INVESTMENT-INCOME> (31)
<REALIZED-GAINS-CURRENT> 17
<APPREC-INCREASE-CURRENT> 280
<NET-CHANGE-FROM-OPS> 267
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 3162
<NUMBER-OF-SHARES-REDEEMED> (325)
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 3103
<ACCUMULATED-NII-PRIOR> (2)
<ACCUMULATED-GAINS-PRIOR> (2)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 14
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 72
<AVERAGE-NET-ASSETS> 2795
<PER-SHARE-NAV-BEGIN> 13.48
<PER-SHARE-NII> (0.11)
<PER-SHARE-GAIN-APPREC> 3.21
<PER-SHARE-DIVIDEND> 0.0
<PER-SHARE-DISTRIBUTIONS> 0.0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 16.58
<EXPENSE-RATIO> 2.50
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 149
<NAME> MANAGED INDEX PORTFOLIO, CLASS C
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 33544
<INVESTMENTS-AT-VALUE> 37067
<RECEIVABLES> 117
<ASSETS-OTHER> 590
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 37773
<PAYABLE-FOR-SECURITIES> 283
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 51
<TOTAL-LIABILITIES> 334
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 2426
<SHARES-COMMON-STOCK> 148
<SHARES-COMMON-PRIOR> 29
<ACCUMULATED-NII-CURRENT> (16)
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 21
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 23
<NET-ASSETS> 2454
<DIVIDEND-INCOME> 20
<INTEREST-INCOME> 0
<OTHER-INCOME> 0
<EXPENSES-NET> 35
<NET-INVESTMENT-INCOME> (15)
<REALIZED-GAINS-CURRENT> 22
<APPREC-INCREASE-CURRENT> 51
<NET-CHANGE-FROM-OPS> 58
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 2219
<NUMBER-OF-SHARES-REDEEMED> (220)
<SHARES-REINVESTED> 0
<NET-CHANGE-IN-ASSETS> 2057
<ACCUMULATED-NII-PRIOR> (1)
<ACCUMULATED-GAINS-PRIOR> (1)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 7
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 36
<AVERAGE-NET-ASSETS> 1418
<PER-SHARE-NAV-BEGIN> 13.52
<PER-SHARE-NII> (0.09)
<PER-SHARE-GAIN-APPREC> 3.19
<PER-SHARE-DIVIDEND> 0.0
<PER-SHARE-DISTRIBUTIONS> 0.0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 16.62
<EXPENSE-RATIO> 2.50
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000356682
<NAME> CALVERT SOCIAL INVESTMENT FUND
<SERIES>
<NUMBER> 150
<NAME> MANAGED INDEX PORTFOLIO, CLASS I
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-1999
<PERIOD-START> APR-01-1999
<PERIOD-END> SEP-30-1999
<INVESTMENTS-AT-COST> 33544
<INVESTMENTS-AT-VALUE> 37067
<RECEIVABLES> 117
<ASSETS-OTHER> 590
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 37773
<PAYABLE-FOR-SECURITIES> 283
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 51
<TOTAL-LIABILITIES> 334
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 16572
<SHARES-COMMON-STOCK> 1104
<SHARES-COMMON-PRIOR> 1100
<ACCUMULATED-NII-CURRENT> 109
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (531)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 2502
<NET-ASSETS> 18652
<DIVIDEND-INCOME> 257
<INTEREST-INCOME> 0
<OTHER-INCOME> 0
<EXPENSES-NET> 138
<NET-INVESTMENT-INCOME> 119
<REALIZED-GAINS-CURRENT> (444)
<APPREC-INCREASE-CURRENT> 4058
<NET-CHANGE-FROM-OPS> 3733
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (50)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 37
<NUMBER-OF-SHARES-REDEEMED> (15)
<SHARES-REINVESTED> 50
<NET-CHANGE-IN-ASSETS> 3755
<ACCUMULATED-NII-PRIOR> 39
<ACCUMULATED-GAINS-PRIOR> (87)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 92
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 148
<AVERAGE-NET-ASSETS> 18345
<PER-SHARE-NAV-BEGIN> 13.54
<PER-SHARE-NII> 0.11
<PER-SHARE-GAIN-APPREC> 3.29
<PER-SHARE-DIVIDEND> (0.05)
<PER-SHARE-DISTRIBUTIONS> 0.0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 16.89
<EXPENSE-RATIO> 0.75
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
