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> 644
<NAME> MANAGED INDEX PORTFOLIO, CLASS I
<MULTIPLIER> 1000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> SEP-30-2000
<PERIOD-START> APR-01-2000
<PERIOD-END> SEP-30-2000
<INVESTMENTS-AT-COST> 44086
<INVESTMENTS-AT-VALUE> 54928
<RECEIVABLES> 44
<ASSETS-OTHER> 135
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 55107
<PAYABLE-FOR-SECURITIES> 124
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 376
<TOTAL-LIABILITIES> 500
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 16594
<SHARES-COMMON-STOCK> 1106
<SHARES-COMMON-PRIOR> 1104
<ACCUMULATED-NII-CURRENT> 137
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> (467)
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 5899
<NET-ASSETS> 22163
<DIVIDEND-INCOME> 236
<INTEREST-INCOME> 0
<OTHER-INCOME> 3
<EXPENSES-NET> 160
<NET-INVESTMENT-INCOME> 78
<REALIZED-GAINS-CURRENT> (467)
<APPREC-INCREASE-CURRENT> 3398
<NET-CHANGE-FROM-OPS> 3008
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 118
<NUMBER-OF-SHARES-REDEEMED> (146)
<SHARES-REINVESTED> 50
<NET-CHANGE-IN-ASSETS> 3030
<ACCUMULATED-NII-PRIOR> 109
<ACCUMULATED-GAINS-PRIOR> (87)
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 107
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 189
<AVERAGE-NET-ASSETS> 21322
<PER-SHARE-NAV-BEGIN> 16.89
<PER-SHARE-NII> 0.07
<PER-SHARE-GAIN-APPREC> 3.13
<PER-SHARE-DIVIDEND> (0.05)
<PER-SHARE-DISTRIBUTIONS> 0.00
<RETURNS-OF-CAPITAL> 0.00
<PER-SHARE-NAV-END> 20.04
<EXPENSE-RATIO> 0.75
[AVG-DEBT-OUTSTANDING] 0
[AVG-DEBT-PER-SHARE] 0
</TABLE>
