<TABLE> <S> <C>
<ARTICLE> 6
<LEGEND>
this schedule contains summary financial information from mason street funds,
inc. index 400 stock fund, 03/31/00 financial statements class a.
</LEGEND>
<CIK> 0001023744
<NAME> MASON STREET FUNDS, INC.
<SERIES>
<NUMBER> 051
<NAME> INDEX 400 STOCK FUND CLASS A
<S> <C>
<PERIOD-TYPE> 12-MOS
<FISCAL-YEAR-END> MAR-31-2000
<PERIOD-START> APR-01-1999
<PERIOD-END> MAR-31-2000
<INVESTMENTS-AT-COST> 29881426
<INVESTMENTS-AT-VALUE> 33165822
<RECEIVABLES> 2425771
<ASSETS-OTHER> 52076
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 35643669
<PAYABLE-FOR-SECURITIES> 647
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 38669
<TOTAL-LIABILITIES> 39316
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 29976789
<SHARES-COMMON-STOCK> 2698508
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 29538
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 2290705
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 3307321
<NET-ASSETS> 35604353
<DIVIDEND-INCOME> 220453
<INTEREST-INCOME> 83345
<OTHER-INCOME> 0
<EXPENSES-NET> 200696
<NET-INVESTMENT-INCOME> 103102
<REALIZED-GAINS-CURRENT> 2457218
<APPREC-INCREASE-CURRENT> 3307321
<NET-CHANGE-FROM-OPS> 5867641
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 121350
<DISTRIBUTIONS-OF-GAINS> 151071
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 2703436
<NUMBER-OF-SHARES-REDEEMED> 31821
<SHARES-REINVESTED> 26393
<NET-CHANGE-IN-ASSETS> 35594353
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 80979
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 336498
<AVERAGE-NET-ASSETS> 0
<PER-SHARE-NAV-BEGIN> 10.0
<PER-SHARE-NII> 0.04
<PER-SHARE-GAIN-APPREC> 1.93
<PER-SHARE-DIVIDEND> 0.05
<PER-SHARE-DISTRIBUTIONS> 0.06
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 11.86
<EXPENSE-RATIO> 0.95
</TABLE>
