<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000727101
<NAME> STATE STREET RESEARCH CAPITAL TRUST
<SERIES>
<NUMBER> 012
<NAME> STATE STREET RESEARCH MID-CAP GROWTH FUND - CLASS B
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> SEP-30-2000
<PERIOD-END> MAR-31-2000
<INVESTMENTS-AT-COST> 873,451,059
<INVESTMENTS-AT-VALUE> 1,112,178,341
<RECEIVABLES> 25,836,441
<ASSETS-OTHER> 40,134
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 1,138,054,916
<PAYABLE-FOR-SECURITIES> 170,000
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 44,186,822
<TOTAL-LIABILITIES> 44,356,822
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 479,823,204
<SHARES-COMMON-STOCK> 23,349,534
<SHARES-COMMON-PRIOR> 24,703,361
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 375,147,608
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 238,727,282
<NET-ASSETS> 1,093,698,094
<DIVIDEND-INCOME> 812,032
<INTEREST-INCOME> 1,726,337
<OTHER-INCOME> 0
<EXPENSES-NET> 8,470,429
<NET-INVESTMENT-INCOME> (5,932,060)
<REALIZED-GAINS-CURRENT> 381,894,168
<APPREC-INCREASE-CURRENT> 11,413,468
<NET-CHANGE-FROM-OPS> 387,375,576
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> (19,305,814)
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 701,822
<NUMBER-OF-SHARES-REDEEMED> (3,264,746)
<SHARES-REINVESTED> 1,209,097
<NET-CHANGE-IN-ASSETS> 312,619,975
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 45,511,935
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 3,503,168
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 8,524,675
<AVERAGE-NET-ASSETS> 964,247,130
<PER-SHARE-NAV-BEGIN> 12.90
<PER-SHARE-NII> (0.13)
<PER-SHARE-GAIN-APPREC> 6.61
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> (0.83)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 18.55
<EXPENSE-RATIO> 2.19
</TABLE>