<PAGE>
NORTHWESTERN MUTUAL LIFE
720 East Wisconsin Avenue
Milwaukee, WI 53202
414-299-2508
March 26, 1998
Securities and Exchange Commission
Division of Investment Management
450 Fifth Street, N.W.
Washington, D.C. 20549
RE: Northwestern Mutual Series Fund, Inc.
SEC File No: 2-89971
EDGAR CIK #: 0000742212
Filing Fee: $57,397.66
Gentlemen:
Enclosed herewith for filing pursuant to Rule 24f-2, under the Investment
Company Act of 1940, is the Rule 24f-2 notice for the investment company
identified above. The filing fee in the amount set forth in the caption above
was submitted directly to the US Treasury at the Mellon Bank in Pittsburgh,
Pennsylvania by wire transfer, as the filing fee for registration of securities
of the issuer pursuant to Rule 24f-2(c) under the Securities Act of 1933. The
deposit of $57,397.66 with the Mellon Bank for the filing fee has been
designated as "Restricted" to this particular filing.
This filing is being effected by direct transmission to the Commission's
EDGAR System. Please call the undersigned with any questions or comments about
this filing.
Very truly yours,
/s/ Sara A. Holm
Paralegal Specialist
Northwestern Mutual Series
Fund, Inc.
<PAGE>
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM 24F-2
Annual Notice of Securities Sold
Pursuant to Rule 24f-2
1. Name and address of issuer:
Northwestern Mutual Series Fund, Inc.
720 East Wisconsin Avenue
Milwaukee, Wisconsin 53202
2. Name of each series or class of funds for which this Form is filed. (If
the Form is being filed for all series and classes of funds of the issuer,
check the box but do not list series or classes):
3. Investment Company Act File Number: 811-3990
Securities Act File Number: 2-89971
4(a). Last day of fiscal year for which this Form is filed:
December 31, 1997
4(b). / / Check box if this Form is being filed late (i.e., more than 90
calendar days after the end of the issuer's fiscal year).
4(c). / / Check box if this is the last time the issuer will be filing this
Form.
5. Calculation of registration fee:
(i) Aggregate sale price of securities
sold during the fiscal year pursuant
to section 24(f): $418,506,693*
-------------
(ii) Aggregate price of securities
redeemed or repurchased during
the fiscal year: $223,938,357#
------------
(iii) Aggregate price of securities redeemed
or repurchased during any prior fiscal
year ending no earlier than October 11,
1995 that were not previously used to
reduce registration fees payable to the
Commission: $ 0
-----
(iv) Total available redemption credits
[add items 5(ii) and 5(iii)]: $223,938,357
------------
(v) Net sales - if item 5(i) is greater
than 5(iv) [subtract item 5(iv) from
item 5(i)]: $194,568,336
------------
(vi) Redemption credits available for use
in future years - if item 5(i) is less
than item 5(iv) [subtract item 5(iv)
from item 5(i)]: $( 0 )
-----
<PAGE>
(vii) Multiplier for determining registration
fee: x.000295
------
(viii) Registration fee due [multiply
item 5(v) by item 5(vii)] (enter "0"
if no fee is due): =$57,397.66
----------
----------
6. Prepaid Shares
If the response to item 5(i) was determined by deducting an amount of
securities that were registered under the Securities Act of 1933 pursuant
to rule 24e-2 as in effect before October 11, 1997, then report the amount
of securities (number of shares or other units) deducted here: 0 . If
there is a number of shares or other units that were registered pursuant to
rule 24e-2 remaining unsold at the end of the fiscal year for which this
form is filed that are available for use by the issuer in future fiscal
years, then state that number here: 0 .
7. Interest due -- if this Form is being filed more than 90 days after the end
of the issuer's fiscal year:
+$ 0
------
8. Total of the amount of the registration fee due plus any interest due [line
5(viii) plus line 7]:
=$57,397.66
----------
----------
9. Date the registration fee and any interest payment was sent to the
Commission's lockbox depository:
Method of Delivery:
/x/ Wire Transfer
/ / Mail or other means
<PAGE>
SIGNATURES
This report has been signed below by the following person on behalf of the
issuer and in the capacity and on the date indicated.
By: /s/
-------------------------------------------------
Barbara E. Courtney
Controller, Northwestern Mutual Series Fund, Inc.
Date: March 26, 1998
* Excludes $832,936,848 of aggregate sale price for securities sold to unmanaged
separate accounts offering interests therein that are registered under the
Securities Act and on which a registration fee has been or will be paid, in
accordance with Instruction C.3 to Form 24f-2.
# Excludes $259,055,625 aggregate sale price for shares excluded in Item 5(i)
above.
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<PAGE>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM NORTHWESTERN
MUTUAL SERIES FUND, INC., AGGRESSIVE GROWTH STOCK FUND, 12/31/97 FINANCIAL
STATEMENTS AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL
STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-START> JAN-01-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 745,200
<INVESTMENTS-AT-VALUE> 1,066,943
<RECEIVABLES> 2,727
<ASSETS-OTHER> 94
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 1,069,764
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 2,696
<TOTAL-LIABILITIES> 2,696
<SENIOR-EQUITY> 705,539
<PAID-IN-CAPITAL-COMMON> 0
<SHARES-COMMON-STOCK> 319,739
<SHARES-COMMON-PRIOR> 277,222
<ACCUMULATED-NII-CURRENT> 390
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 39,778
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 321,361
<NET-ASSETS> 1,067,068
<DIVIDEND-INCOME> 897
<INTEREST-INCOME> 4,707
<OTHER-INCOME> 0
<EXPENSES-NET> 5,004
<NET-INVESTMENT-INCOME> 600
<REALIZED-GAINS-CURRENT> 44,968
<APPREC-INCREASE-CURRENT> 82,701
<NET-CHANGE-FROM-OPS> 128,269
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 0
<DISTRIBUTIONS-OF-GAINS> 57,365
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 35,663
<NUMBER-OF-SHARES-REDEEMED> 14,059
<SHARES-REINVESTED> 20,913
<NET-CHANGE-IN-ASSETS> 195,142
<ACCUMULATED-NII-PRIOR> (210)
<ACCUMULATED-GAINS-PRIOR> 52,175
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 0
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 5,034
<AVERAGE-NET-ASSETS> 0
<PER-SHARE-NAV-BEGIN> 3.15
<PER-SHARE-NII> 0
<PER-SHARE-GAIN-APPREC> .39
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> .20
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 3.34
<EXPENSE-RATIO> .53
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<PAGE>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM NORTHWESTERN
MUTUAL SERIES FUND, INC., INTERNATIONAL EQUITY FUND, 12/31/97 FINANCIAL
STATEMENTS AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL
STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-START> JAN-01-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 543,741
<INVESTMENTS-AT-VALUE> 657,718
<RECEIVABLES> 2,731
<ASSETS-OTHER> 1,814
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 662,263
<PAYABLE-FOR-SECURITIES> 802
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 1,611
<TOTAL-LIABILITIES> 2,413
<SENIOR-EQUITY> 507,045
<PAID-IN-CAPITAL-COMMON> 0
<SHARES-COMMON-STOCK> 390,790
<SHARES-COMMON-PRIOR> 324,246
<ACCUMULATED-NII-CURRENT> 16,682
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 22,191
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 113,152
<NET-ASSETS> 659,850
<DIVIDEND-INCOME> 18,717
<INTEREST-INCOME> 2,883
<OTHER-INCOME> 0
<EXPENSES-NET> 4,755
<NET-INVESTMENT-INCOME> 16,845
<REALIZED-GAINS-CURRENT> 22,636
<APPREC-INCREASE-CURRENT> 25,359
<NET-CHANGE-FROM-OPS> 64,840
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 12,704
<DISTRIBUTIONS-OF-GAINS> 7,542
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 66,307
<NUMBER-OF-SHARES-REDEEMED> 12,361
<SHARES-REINVESTED> 12,598
<NET-CHANGE-IN-ASSETS> 54,661
<ACCUMULATED-NII-PRIOR> 12,614
<ACCUMULATED-GAINS-PRIOR> 7,391
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 0
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 4,755
<AVERAGE-NET-ASSETS> 0
<PER-SHARE-NAV-BEGIN> 1.56
<PER-SHARE-NII> .04
<PER-SHARE-GAIN-APPREC> .15
<PER-SHARE-DIVIDEND> .04
<PER-SHARE-DISTRIBUTIONS> .02
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.69
<EXPENSE-RATIO> .77
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<PAGE>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM NORTHWESTERN
MUTUAL SERIES FUND, INC., GROWTH STOCK FUND, 12/31/97 FINANCIAL STATEMENTS AND
IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANICAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-START> JAN-01-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 170,190
<INVESTMENTS-AT-VALUE> 242,686
<RECEIVABLES> 930
<ASSETS-OTHER> 51
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 243,667
<PAYABLE-FOR-SECURITIES> 446
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 150
<TOTAL-LIABILITIES> 596
<SENIOR-EQUITY> 166,515
<PAID-IN-CAPITAL-COMMON> 0
<SHARES-COMMON-STOCK> 134,273
<SHARES-COMMON-PRIOR> 116,463
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 4,060
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 72,496
<NET-ASSETS> 243,071
<DIVIDEND-INCOME> 2,558
<INTEREST-INCOME> 1,160
<OTHER-INCOME> 0
<EXPENSES-NET> 1,049
<NET-INVESTMENT-INCOME> 2,669
<REALIZED-GAINS-CURRENT> 11,942
<APPREC-INCREASE-CURRENT> 42,501
<NET-CHANGE-FROM-OPS> 57,112
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 2,685
<DISTRIBUTIONS-OF-GAINS> 8,527
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 42,594
<NUMBER-OF-SHARES-REDEEMED> 31,206
<SHARES-REINVESTED> 6,422
<NET-CHANGE-IN-ASSETS> 72,589
<ACCUMULATED-NII-PRIOR> 1,067
<ACCUMULATED-GAINS-PRIOR> 5,039
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 0
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 1,066
<AVERAGE-NET-ASSETS> 0
<PER-SHARE-NAV-BEGIN> 1.46
<PER-SHARE-NII> .02
<PER-SHARE-GAIN-APPREC> .42
<PER-SHARE-DIVIDEND> .02
<PER-SHARE-DISTRIBUTIONS> .07
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.81
<EXPENSE-RATIO> .49
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<PAGE>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM
NORTHWESTERN MUTUAL SERIES FUND, INC., GROWTH AND INCOME STOCK FUND,
12/31/97 FINANCIAL STATEMENTS AND IS QUALIFIED IN ITS ENTIRETY BY
REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-START> JAN-01-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 342,839
<INVESTMENTS-AT-VALUE> 370,014
<RECEIVABLES> 5,500
<ASSETS-OTHER> 82
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 375,596
<PAYABLE-FOR-SECURITIES> 3,215
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 446
<TOTAL-LIABILITIES> 3,661
<SENIOR-EQUITY> 344,245
<PAID-IN-CAPITAL-COMMON> 0
<SHARES-COMMON-STOCK> 279,536
<SHARES-COMMON-PRIOR> 177,728
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 515
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 27,175
<NET-ASSETS> 371,935
<DIVIDEND-INCOME> 4,542
<INTEREST-INCOME> 450
<OTHER-INCOME> 0
<EXPENSES-NET> 1,818
<NET-INVESTMENT-INCOME> 3,174
<REALIZED-GAINS-CURRENT> 72,633
<APPREC-INCREASE-CURRENT> 2,850
<NET-CHANGE-FROM-OPS> 78,651
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 3,200
<DISTRIBUTIONS-OF-GAINS> 78,180
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 75,470
<NUMBER-OF-SHARES-REDEEMED> 35,535
<SHARES-REINVESTED> 61,873
<NET-CHANGE-IN-ASSETS> 137,751
<ACCUMULATED-NII-PRIOR> 2,654
<ACCUMULATED-GAINS-PRIOR> 21,066
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 0
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 1,849
<AVERAGE-NET-ASSETS> 0
<PER-SHARE-NAV-BEGIN> .32
<PER-SHARE-NII> .01
<PER-SHARE-GAIN-APPREC> .37
<PER-SHARE-DIVIDEND> .01
<PER-SHARE-DISTRIBUTIONS> .36
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.33
<EXPENSE-RATIO> .60
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<PAGE>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM NORTHWESTERN
MUTUAL SERIES FUND, INC., INDEX 500 STOCK FUND, 12/31/97 FINANCIAL STATEMENTS
AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-START> JAN-01-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 713,039
<INVESTMENTS-AT-VALUE> 1,152,781
<RECEIVABLES> 1,726
<ASSETS-OTHER> 50
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 1,154,557
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 1,700
<TOTAL-LIABILITIES> 1,700
<SENIOR-EQUITY> 667,337
<PAID-IN-CAPITAL-COMMON> 0
<SHARES-COMMON-STOCK> 436,104
<SHARES-COMMON-PRIOR> 360,059
<ACCUMULATED-NII-CURRENT> 17,811
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 27,298
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 440,411
<NET-ASSETS> 1,152,857
<DIVIDEND-INCOME> 16,013
<INTEREST-INCOME> 3,795
<OTHER-INCOME> 0
<EXPENSES-NET> 1,997
<NET-INVESTMENT-INCOME> 17,811
<REALIZED-GAINS-CURRENT> 27,640
<APPREC-INCREASE-CURRENT> 219,972
<NET-CHANGE-FROM-OPS> 265,423
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 13,866
<DISTRIBUTIONS-OF-GAINS> 16,994
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 75,307
<NUMBER-OF-SHARES-REDEEMED> 12,917
<SHARES-REINVESTED> 13,655
<NET-CHANGE-IN-ASSETS> 412,791
<ACCUMULATED-NII-PRIOR> 13,866
<ACCUMULATED-GAINS-PRIOR> 17,014
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 0
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 2,045
<AVERAGE-NET-ASSETS> 0
<PER-SHARE-NAV-BEGIN> 2.06
<PER-SHARE-NII> .04
<PER-SHARE-GAIN-APPREC> .62
<PER-SHARE-DIVIDEND> .04
<PER-SHARE-DISTRIBUTIONS> .04
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 2.64
<EXPENSE-RATIO> 1.86
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<PAGE>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANICIAL INFORMATION EXTRACTED FROM
NORTHWESTERN MUTUAL SERIES FUND, INC., BALANCED FUND, 12/31/97 FINANCIAL
STATEMENTS AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL
STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-START> JAN-01-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 1,960,305
<INVESTMENTS-AT-VALUE> 2,774,619
<RECEIVABLES> 35,430
<ASSETS-OTHER> 3,616
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 2,813,665
<PAYABLE-FOR-SECURITIES> 6,648
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 18,523
<TOTAL-LIABILITIES> 25,171
<SENIOR-EQUITY> 1,794,233
<PAID-IN-CAPITAL-COMMON> 0
<SHARES-COMMON-STOCK> 1,400,746
<SHARES-COMMON-PRIOR> 1,353,952
<ACCUMULATED-NII-CURRENT> 94,962
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 85,588
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 813,711
<NET-ASSETS> 2,788,494
<DIVIDEND-INCOME> 25,121
<INTEREST-INCOME> 77,592
<OTHER-INCOME> 0
<EXPENSES-NET> 7,727
<NET-INVESTMENT-INCOME> 94,986
<REALIZED-GAINS-CURRENT> 83,356
<APPREC-INCREASE-CURRENT> 318,351
<NET-CHANGE-FROM-OPS> 496,693
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 86,698
<DISTRIBUTIONS-OF-GAINS> 29,228
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 42,694
<NUMBER-OF-SHARES-REDEEMED> 61,284
<SHARES-REINVESTED> 65,384
<NET-CHANGE-IN-ASSETS> 462,260
<ACCUMULATED-NII-PRIOR> 86,649
<ACCUMULATED-GAINS-PRIOR> 27,969
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 0
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 7,727
<AVERAGE-NET-ASSETS> 0
<PER-SHARE-NAV-BEGIN> 1.72
<PER-SHARE-NII> .07
<PER-SHARE-GAIN-APPREC> .28
<PER-SHARE-DIVIDEND> .06
<PER-SHARE-DISTRIBUTIONS> .02
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 1.99
<EXPENSE-RATIO> .30
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<PAGE>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM NORTHWESTERN
MUTUAL SERIES FUND, INC., HIGH YIELD BOND FUND, 12/31/97 FINANCIAL STATEMENTS
AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-START> JAN-01-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 149,252
<INVESTMENTS-AT-VALUE> 150,865
<RECEIVABLES> 2,721
<ASSETS-OTHER> 0
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 153,586
<PAYABLE-FOR-SECURITIES> 440
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 108
<TOTAL-LIABILITIES> 548
<SENIOR-EQUITY> 151,568
<PAID-IN-CAPITAL-COMMON> 0
<SHARES-COMMON-STOCK> 143,917
<SHARES-COMMON-PRIOR> 85,421
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 143
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 1,613
<NET-ASSETS> 153,038
<DIVIDEND-INCOME> 2,593
<INTEREST-INCOME> 10,660
<OTHER-INCOME> 0
<EXPENSES-NET> 692
<NET-INVESTMENT-INCOME> 12,561
<REALIZED-GAINS-CURRENT> 7,437
<APPREC-INCREASE-CURRENT> (1,416)
<NET-CHANGE-FROM-OPS> 18,582
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 16,554
<DISTRIBUTIONS-OF-GAINS> 8,429
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 48,820
<NUMBER-OF-SHARES-REDEEMED> 13,489
<SHARES-REINVESTED> 23,165
<NET-CHANGE-IN-ASSETS> 59,160
<ACCUMULATED-NII-PRIOR> 6,867
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<OVERDISTRIB-NII-PRIOR> 297
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<GROSS-EXPENSE> 706
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<PER-SHARE-NAV-BEGIN> 1.10
<PER-SHARE-NII> .11
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<PER-SHARE-DIVIDEND> .14
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<PER-SHARE-NAV-END> 1.06
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<AVG-DEBT-OUTSTANDING> 0
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</TABLE>
WARNING: THE EDGAR SYSTEM ENCOUNTERED ERROR(S) WHILE PROCESSING THIS SCHEDULE.
<TABLE> <S> <C>
<PAGE>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM NORTHWESTERN
MUTUAL SERIES FUND, INC., SELECT BOND FUND, 12/31/97 FINANCIAL STATEMENTS AND IS
QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-START> JAN-01-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 234,165
<INVESTMENTS-AT-VALUE> 238,210
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<TOTAL-ASSETS> 258,093
<PAYABLE-FOR-SECURITIES> 1,171
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 12,087
<TOTAL-LIABILITIES> 13,258
<SENIOR-EQUITY> 223,542
<PAID-IN-CAPITAL-COMMON> 0
<SHARES-COMMON-STOCK> 194,772
<SHARES-COMMON-PRIOR> 175,166
<ACCUMULATED-NII-CURRENT> 15,722
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 2,050
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 3,521
<NET-ASSETS> 244,835
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 16,343
<OTHER-INCOME> 0
<EXPENSES-NET> 667
<NET-INVESTMENT-INCOME> 15,676
<REALIZED-GAINS-CURRENT> 2,865
<APPREC-INCREASE-CURRENT> 1,736
<NET-CHANGE-FROM-OPS> 20,277
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> 13,300
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 26,095
<NUMBER-OF-SHARES-REDEEMED> 17,885
<SHARES-REINVESTED> 11,396
<NET-CHANGE-IN-ASSETS> 30,502
<ACCUMULATED-NII-PRIOR> 13,288
<ACCUMULATED-GAINS-PRIOR> 569
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 0
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 667
<AVERAGE-NET-ASSETS> 0
<PER-SHARE-NAV-BEGIN> 1.22
<PER-SHARE-NII> .08
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<PER-SHARE-DIVIDEND> .08
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<PER-SHARE-NAV-END> 1.26
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<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<PAGE>
<ARTICLE> 6
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM NORTHWESTERN
MUTUAL SERIES FUND, INC., MONEY MARKET FUND, 12/31/97 FINANCIAL STATEMENTS AND
IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
<S> <C>
<PERIOD-TYPE> YEAR
<FISCAL-YEAR-END> DEC-31-1997
<PERIOD-START> JAN-01-1997
<PERIOD-END> DEC-31-1997
<INVESTMENTS-AT-COST> 193,630
<INVESTMENTS-AT-VALUE> 193,630
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<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 168
<TOTAL-LIABILITIES> 168
<SENIOR-EQUITY> 194,470
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<SHARES-COMMON-STOCK> 194,494
<SHARES-COMMON-PRIOR> 176,314
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> 0
<NET-ASSETS> 194,470
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 10,433
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<EXPENSES-NET> 555
<NET-INVESTMENT-INCOME> 9,878
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<APPREC-INCREASE-CURRENT> 0
<NET-CHANGE-FROM-OPS> 9,878
<EQUALIZATION> 0
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<DISTRIBUTIONS-OF-GAINS> 0
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<NUMBER-OF-SHARES-SOLD> 130,864
<NUMBER-OF-SHARES-REDEEMED> 122,562
<SHARES-REINVESTED> 9,878
<NET-CHANGE-IN-ASSETS> 18,172
<ACCUMULATED-NII-PRIOR> 7,576
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<OVERDISTRIB-NII-PRIOR> 0
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<GROSS-ADVISORY-FEES> 0
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 555
<AVERAGE-NET-ASSETS> 0
<PER-SHARE-NAV-BEGIN> 1.00
<PER-SHARE-NII> .05
<PER-SHARE-GAIN-APPREC> 0
<PER-SHARE-DIVIDEND> .05
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<PER-SHARE-NAV-END> 1.00
<EXPENSE-RATIO> .30
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
