<PAGE> PAGE 1
000 A000000 07/31/97
000 C000000 0000225604
000 D000000 N
000 E000000 NF
000 F000000 Y
000 G000000 N
000 H000000 N
000 I000000 3.0.a
000 J000000 A
001 A000000 MFS SERIES TRUST III
001 B000000 811-2794
001 C000000 6179545000
002 A000000 500 BOYLSTON STREET
002 B000000 BOSTON
002 C000000 MA
002 D010000 02116
003 000000 N
004 000000 N
005 000000 N
006 000000 N
007 A000000 Y
007 B000000 2
007 C010100 1
007 C020100 MFS HIGH INCOME FUND
007 C030100 N
007 C010200 2
007 C020200 MFS MUNICIPAL HIGH INCOME FUND
007 C030200 N
007 C010300 3
007 C010400 4
007 C010500 5
007 C010600 6
007 C010700 7
007 C010800 8
007 C010900 9
007 C011000 10
008 A00AA01 MASSACHUSETTS FINANCIAL SERVICE COMPANY
008 B00AA01 A
008 C00AA01 801-17352
008 D01AA01 BOSTON
008 D02AA01 MA
008 D03AA01 02116
010 A00AA01 MASSACHUSETTS FINANCIAL SERVICES COMPANY
010 B00AA01 801-17352
010 C01AA01 BOSTON
010 C02AA01 MA
010 C03AA01 02116
011 A00AA01 MFS FUND DISTRIBUTORS, INC.
011 B00AA01 8-27864
011 C01AA01 BOSTON
011 C02AA01 MA
<PAGE> PAGE 2
011 C03AA01 02116
012 A00AA01 MFS SERVICE CENTER, INC.
012 B00AA01 84-1316
012 C01AA01 BOSTON
012 C02AA01 MA
012 C03AA01 02116
018 00AA00 Y
019 A00AA00 Y
019 B00AA00 52
019 C00AA00 MASSFINSER
020 A000001 BEAR STEARNS SECURITIES
020 B000001 00-0000000
020 C000001 9
020 A000002 MORGAN STANLEY
020 B000002 13-2655998
020 C000002 2
020 A000003 FURMAN,SELZ,MAGERDIETZ
020 B000003 00-0000000
020 C000003 1
020 C000004 0
020 C000005 0
020 C000006 0
020 C000007 0
020 C000008 0
020 C000009 0
020 C000010 0
021 000000 12
022 A000001 GENERAL ELECTRIC CAP CORP.
022 B000001 00-0000000
022 C000001 342858
022 D000001 6146
022 A000002 PAINE WEBBER INC.
022 B000002 13-2638166
022 C000002 125651
022 D000002 118916
022 A000003 CARROLL MC ENTEE
022 B000003 00-0000000
022 C000003 102430
022 D000003 111266
022 A000004 EXCHANGE OFFER
022 B000004 00-0000000
022 C000004 100605
022 D000004 87125
022 A000005 MORGAN STANLEY
022 B000005 13-2655998
022 C000005 81275
022 D000005 101620
022 A000006 GOLDMAN SACHS
022 B000006 13-5108880
022 C000006 130980
022 D000006 36898
<PAGE> PAGE 3
022 A000007 MORGAN ( J.P.) SECURITIES
022 B000007 13-3224016
022 C000007 87812
022 D000007 55236
022 A000008 PRUDENTIAL SECURITIES
022 B000008 22-2347336
022 C000008 92854
022 D000008 30366
022 A000009 DLJ FIXED INCOME
022 B000009 00-0000000
022 C000009 69629
022 D000009 46467
022 A000010 M L PIERCE FENNER SMITH
022 B000010 00-0000000
022 C000010 52445
022 D000010 46295
023 C000000 1934347
023 D000000 1028679
026 A000000 Y
026 B000000 Y
026 C000000 N
026 D000000 Y
026 E000000 N
026 F000000 N
026 G010000 N
026 G020000 N
026 H000000 N
027 000000 Y
054 A00AA00 Y
054 B00AA00 N
054 C00AA00 N
054 D00AA00 N
054 E00AA00 N
054 F00AA00 N
054 G00AA00 N
054 H00AA00 Y
054 I00AA00 N
054 J00AA00 Y
054 K00AA00 N
054 L00AA00 N
054 M00AA00 Y
054 N00AA00 N
054 O00AA00 N
066 A00AA00 N
067 00AA00 N
068 A00AA00 N
068 B00AA00 N
069 00AA00 N
077 A000000 Y
077 D000000 Y
078 000000 N
<PAGE> PAGE 4
080 A00AA00 NATIONAL UNION INSURANCE CO.
080 B00AA00 ICI MUTUAL
080 C00AA00 0
081 B00AA00 0
082 B00AA00 0
083 B00AA00 0
084 B00AA00 0
086 A010000 0
086 A020000 0
086 B010000 0
086 B020000 0
086 C010000 0
086 C020000 0
086 D010000 0
086 D020000 0
086 E010000 0
086 E020000 0
086 F010000 0
086 F020000 0
013 A000101 DELOITTE & TOUCHE LLP
013 B010101 BOSTON
013 B020101 MA
013 B030101 02110
015 A000101 STATE STREET BANK AND TRUST COMPANY
015 B000101 C
015 C010101 BOSTON
015 C020101 MA
015 C030101 02110
015 E010101 X
015 A000102 CHASE MANHATTAN BANK, N.A.
015 B000102 S
015 C010102 NEW YORK
015 C020102 NY
015 C030102 10081
015 E040102 X
015 A000103 THE BANK OF NEW YORK
015 B000103 S
015 C010103 NEW YORK
015 C020103 NY
015 C030103 10286
015 E010103 X
024 000100 Y
025 A000101 GENERAL ELECTRIC CAPITAL CORP
025 B000101 00-0000000
025 C000101 D
025 D000101 7780
025 D000102 0
025 D000103 0
025 D000104 0
025 D000105 0
025 D000106 0
<PAGE> PAGE 5
025 D000107 0
025 D000108 0
028 A010100 34842
028 A020100 4149
028 A030100 0
028 A040100 19231
028 B010100 24506
028 B020100 3685
028 B030100 0
028 B040100 104243
028 C010100 78813
028 C020100 3642
028 C030100 0
028 C040100 44017
028 D010100 79143
028 D020100 4092
028 D030100 0
028 D040100 45361
028 E010100 39313
028 E020100 4245
028 E030100 0
028 E040100 23999
028 F010100 36624
028 F020100 4247
028 F030100 0
028 F040100 31870
028 G010100 293241
028 G020100 24060
028 G030100 0
028 G040100 268721
028 H000100 144881
029 000100 Y
030 A000100 764
030 B000100 4.75
030 C000100 0.00
031 A000100 117
031 B000100 0
032 000100 647
033 000100 0
034 000100 Y
035 000100 204
036 A000100 N
036 B000100 0
037 000100 N
038 000100 0
039 000100 N
040 000100 Y
041 000100 Y
042 A000100 0
042 B000100 0
042 C000100 52
<PAGE> PAGE 6
042 D000100 48
042 E000100 0
042 F000100 0
042 G000100 0
042 H000100 0
043 000100 2895
044 000100 0
045 000100 Y
046 000100 N
047 000100 N
048 000100 0.000
048 A010100 0
048 A020100 0.000
048 B010100 0
048 B020100 0.000
048 C010100 0
048 C020100 0.000
048 D010100 0
048 D020100 0.000
048 E010100 0
048 E020100 0.000
048 F010100 0
048 F020100 0.000
048 G010100 0
048 G020100 0.000
048 H010100 0
048 H020100 0.000
048 I010100 0
048 I020100 0.000
048 J010100 0
048 J020100 0.000
048 K010100 0
048 K020100 0.000
049 000100 N
050 000100 Y
051 000100 N
052 000100 N
053 A000100 Y
053 B000100 N
053 C000100 Y
055 A000100 Y
055 B000100 N
056 000100 Y
057 000100 N
058 A000100 N
059 000100 Y
060 A000100 Y
060 B000100 Y
061 000100 1000
062 A000100 Y
062 B000100 0.0
<PAGE> PAGE 7
062 C000100 0.0
062 D000100 0.0
062 E000100 0.0
062 F000100 0.0
062 G000100 0.0
062 H000100 0.0
062 I000100 0.0
062 J000100 0.0
062 K000100 0.0
062 L000100 0.7
062 M000100 0.0
062 N000100 0.0
062 O000100 0.0
062 P000100 87.6
062 Q000100 3.0
062 R000100 7.3
063 A000100 0
063 B000100 8.2
064 A000100 N
064 B000100 N
070 A010100 Y
070 A020100 N
070 B010100 N
070 B020100 N
070 C010100 Y
070 C020100 N
070 D010100 N
070 D020100 N
070 E010100 Y
070 E020100 N
070 F010100 N
070 F020100 N
070 G010100 Y
070 G020100 N
070 H010100 N
070 H020100 N
070 I010100 N
070 I020100 N
070 J010100 Y
070 J020100 Y
070 K010100 Y
070 K020100 N
070 L010100 Y
070 L020100 Y
070 M010100 Y
070 M020100 N
070 N010100 Y
070 N020100 N
070 O010100 Y
070 O020100 N
070 P010100 Y
<PAGE> PAGE 8
070 P020100 N
070 Q010100 N
070 Q020100 N
070 R010100 N
070 R020100 N
071 A000100 666726
071 B000100 592898
071 C000100 966298
071 D000100 64
072 A000100 6
072 B000100 48116
072 C000100 1513
072 D000100 0
072 E000100 0
072 F000100 2302
072 G000100 64
072 H000100 0
072 I000100 655
072 J000100 195
072 K000100 90
072 L000100 39
072 M000100 38
072 N000100 0
072 O000100 0
072 P000100 0
072 Q000100 0
072 R000100 28
072 S000100 4
072 T000100 2895
072 U000100 0
072 V000100 0
072 W000100 267
072 X000100 6577
072 Y000100 353
072 Z000100 43405
072AA000100 15956
072BB000100 0
072CC010100 14461
072CC020100 0
072DD010100 29184
072DD020100 12370
072EE000100 0
073 A010100 0.2300
073 A020100 0.2500
073 B000100 0.0000
073 C000100 0.0000
074 A000100 5
074 B000100 0
074 C000100 7780
074 D000100 989834
074 E000100 66010
<PAGE> PAGE 9
074 F000100 5168
074 G000100 0
074 H000100 0
074 I000100 0
074 J000100 38141
074 K000100 0
074 L000100 25621
074 M000100 9
074 N000100 1132568
074 O000100 36573
074 P000100 300
074 Q000100 0
074 R010100 0
074 R020100 0
074 R030100 0
074 R040100 11379
074 S000100 0
074 T000100 1084316
074 U010100 127050
074 U020100 61756
074 V010100 5.50
074 V020100 5.51
074 W000100 0.0000
074 X000100 49641
074 Y000100 0
075 A000100 0
075 B000100 1013655
076 000100 0.00
013 A000201 ERNST & YOUNG LLP
013 B010201 BOSTON
013 B020201 MA
013 B030201 02116
015 A000201 STATE STREET BANK AND TRUST COMPANY
015 B000201 C
015 C010201 BOSTON
015 C020201 MA
015 C030201 02110
015 E010201 X
015 A000202 THE BANK OF NEW YORK
015 B000202 S
015 C010202 NEW YORK
015 C020202 NY
015 C030202 10286
015 E010202 X
015 A000203 CHEMICAL BANK
015 B000203 S
015 C010203 NEW YORK
015 C020203 NY
015 C030203 10041
015 E010203 X
015 A000204 MORGAN GUARANTY TRUST COMPANY
<PAGE> PAGE 10
015 B000204 S
015 C010204 NEW YORK
015 C020204 NY
015 C030204 10015
015 E010204 X
015 A000205 BANKERS TRUST COMPANY
015 B000205 S
015 C010205 NEW YORK
015 C020205 NY
015 C030205 10015
015 E010205 X
024 000200 N
025 D000201 0
025 D000202 0
025 D000203 0
025 D000204 0
025 D000205 0
025 D000206 0
025 D000207 0
025 D000208 0
028 A010200 21272
028 A020200 2261
028 A030200 0
028 A040200 13629
028 B010200 22729
028 B020200 2272
028 B030200 0
028 B040200 14948
028 C010200 24074
028 C020200 2287
028 C030200 0
028 C040200 16008
028 D010200 40707
028 D020200 2245
028 D030200 0
028 D040200 15118
028 E010200 33244
028 E020200 2436
028 E030200 0
028 E040200 13913
028 F010200 38033
028 F020200 2366
028 F030200 0
028 F040200 12856
028 G010200 180059
028 G020200 13867
028 G030200 0
028 G040200 86472
028 H000200 113000
029 000200 Y
030 A000200 2766
<PAGE> PAGE 11
030 B000200 4.75
030 C000200 0.00
031 A000200 472
031 B000200 0
032 000200 2294
033 000200 0
034 000200 Y
035 000200 141
036 A000200 N
036 B000200 0
037 000200 N
038 000200 0
039 000200 N
040 000200 Y
041 000200 Y
042 A000200 0
042 B000200 0
042 C000200 93
042 D000200 7
042 E000200 0
042 F000200 0
042 G000200 0
042 H000200 0
043 000200 608
044 000200 0
045 000200 Y
046 000200 N
047 000200 N
048 000200 0.000
048 A010200 0
048 A020200 0.000
048 B010200 0
048 B020200 0.000
048 C010200 0
048 C020200 0.000
048 D010200 0
048 D020200 0.000
048 E010200 0
048 E020200 0.000
048 F010200 0
048 F020200 0.000
048 G010200 0
048 G020200 0.000
048 H010200 0
048 H020200 0.000
048 I010200 0
048 I020200 0.000
048 J010200 0
048 J020200 0.000
048 K010200 0
048 K020200 0.000
<PAGE> PAGE 12
049 000200 N
050 000200 Y
051 000200 N
052 000200 N
053 A000200 Y
053 B000200 N
053 C000200 Y
055 A000200 N
055 B000200 N
056 000200 Y
057 000200 N
058 A000200 N
059 000200 Y
060 A000200 N
060 B000200 N
061 000200 1000
062 A000200 Y
062 B000200 0.0
062 C000200 0.0
062 D000200 0.0
062 E000200 0.0
062 F000200 0.0
062 G000200 0.0
062 H000200 0.0
062 I000200 0.0
062 J000200 0.0
062 K000200 0.0
062 L000200 1.8
062 M000200 0.0
062 N000200 0.0
062 O000200 96.4
062 P000200 0.0
062 Q000200 0.0
062 R000200 0.0
063 A000200 0
063 B000200 20.3
064 A000200 Y
064 B000200 Y
065 000200 N
070 A010200 Y
070 A020200 N
070 B010200 N
070 B020200 N
070 C010200 Y
070 C020200 N
070 D010200 N
070 D020200 N
070 E010200 Y
070 E020200 N
070 F010200 N
070 F020200 N
<PAGE> PAGE 13
070 G010200 Y
070 G020200 N
070 H010200 N
070 H020200 N
070 I010200 N
070 I020200 N
070 J010200 Y
070 J020200 Y
070 K010200 Y
070 K020200 N
070 L010200 N
070 L020200 N
070 M010200 N
070 M020200 N
070 N010200 Y
070 N020200 N
070 O010200 Y
070 O020200 N
070 P010200 Y
070 P020200 N
070 Q010200 N
070 Q020200 N
070 R010200 N
070 R020200 N
071 A000200 192291
071 B000200 114150
071 C000200 1127283
071 D000200 10
072 A000200 6
072 B000200 43643
072 C000200 0
072 D000200 0
072 E000200 0
072 F000200 3787
072 G000200 72
072 H000200 0
072 I000200 742
072 J000200 189
072 K000200 43
072 L000200 31
072 M000200 35
072 N000200 0
072 O000200 0
072 P000200 0
072 Q000200 0
072 R000200 18
072 S000200 18
072 T000200 640
072 U000200 0
072 V000200 0
072 W000200 251
<PAGE> PAGE 14
072 X000200 5826
072 Y000200 158
072 Z000200 37975
072AA000200 0
072BB000200 24416
072CC010200 48155
072CC020200 0
072DD010200 33714
072DD020200 4451
072EE000200 0
073 A010200 0.2900
073 A020200 0.2600
073 B000200 0.0000
073 C000200 0.0000
074 A000200 44
074 B000200 0
074 C000200 23000
074 D000200 1200353
074 E000200 0
074 F000200 0
074 G000200 0
074 H000200 0
074 I000200 0
074 J000200 5916
074 K000200 0
074 L000200 24964
074 M000200 10
074 N000200 1254287
074 O000200 0
074 P000200 91
074 Q000200 0
074 R010200 0
074 R020200 0
074 R030200 0
074 R040200 9042
074 S000200 0
074 T000200 1245154
074 U010200 118658
074 U020200 21244
074 V010200 8.90
074 V020200 8.91
074 W000200 0.0000
074 X000200 31814
074 Y000200 0
075 A000200 0
075 B000200 1147457
076 000200 0.00
SIGNATURE JAMES O. YOST
TITLE ASSISTANT TREASURER
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 011
<NAME> MFS HIGH INCOME FUND CLASS A
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1998
<PERIOD-START> FEB-01-1997
<PERIOD-END> JUL-31-1997
<INVESTMENTS-AT-COST> 1028795832
<INVESTMENTS-AT-VALUE> 1068792355
<RECEIVABLES> 63761535
<ASSETS-OTHER> 8714
<OTHER-ITEMS-ASSETS> 4952
<TOTAL-ASSETS> 1132567556
<PAYABLE-FOR-SECURITIES> 36573443
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 11678262
<TOTAL-LIABILITIES> 48251705
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1300371257
<SHARES-COMMON-STOCK> 127049766
<SHARES-COMMON-PRIOR> 125638629
<ACCUMULATED-NII-CURRENT> 2098105
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (258150034)
<ACCUM-APPREC-OR-DEPREC> 39996523
<NET-ASSETS> 1084315851
<DIVIDEND-INCOME> 1512918
<INTEREST-INCOME> 48116048
<OTHER-INCOME> 0
<EXPENSES-NET> (6224107)
<NET-INVESTMENT-INCOME> 43404859
<REALIZED-GAINS-CURRENT> 15956458
<APPREC-INCREASE-CURRENT> 14461469
<NET-CHANGE-FROM-OPS> 73822786
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (29184016)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 27252361
<NUMBER-OF-SHARES-REDEEMED> (28968872)
<SHARES-REINVESTED> 3127648
<NET-CHANGE-IN-ASSETS> 80018493
<ACCUMULATED-NII-PRIOR> 1677232
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> (274106492)
<GROSS-ADVISORY-FEES> 2302327
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 6577525
<AVERAGE-NET-ASSETS> 1013654560
<PER-SHARE-NAV-BEGIN> 5.35
<PER-SHARE-NII> 0.24
<PER-SHARE-GAIN-APPREC> 0.14
<PER-SHARE-DIVIDEND> (0.23)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 5.50
<EXPENSE-RATIO> 1.09
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 012
<NAME> MFS HIGH INCOME FUND CLASS B
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1998
<PERIOD-START> FEB-01-1997
<PERIOD-END> JUL-31-1997
<INVESTMENTS-AT-COST> 1028795832
<INVESTMENTS-AT-VALUE> 1068792355
<RECEIVABLES> 63761535
<ASSETS-OTHER> 8714
<OTHER-ITEMS-ASSETS> 4952
<TOTAL-ASSETS> 1132567556
<PAYABLE-FOR-SECURITIES> 36573443
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 11678262
<TOTAL-LIABILITIES> 48251705
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1300371257
<SHARES-COMMON-STOCK> 61756248
<SHARES-COMMON-PRIOR> 56215947
<ACCUMULATED-NII-CURRENT> 2098105
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (258150034)
<ACCUM-APPREC-OR-DEPREC> 39996523
<NET-ASSETS> 1084315851
<DIVIDEND-INCOME> 1512918
<INTEREST-INCOME> 48116048
<OTHER-INCOME> 0
<EXPENSES-NET> (6224107)
<NET-INVESTMENT-INCOME> 43404859
<REALIZED-GAINS-CURRENT> 15956458
<APPREC-INCREASE-CURRENT> 14461469
<NET-CHANGE-FROM-OPS> 73822786
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (12369722)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 23760288
<NUMBER-OF-SHARES-REDEEMED> (19411590)
<SHARES-REINVESTED> 1191603
<NET-CHANGE-IN-ASSETS> 80018493
<ACCUMULATED-NII-PRIOR> 1677232
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> (274106492)
<GROSS-ADVISORY-FEES> 2302327
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 6577525
<AVERAGE-NET-ASSETS> 1013654560
<PER-SHARE-NAV-BEGIN> 5.35
<PER-SHARE-NII> 0.22
<PER-SHARE-GAIN-APPREC> 0.19
<PER-SHARE-DIVIDEND> (0.25)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 5.51
<EXPENSE-RATIO> 1.74
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 013
<NAME> MFS HIGH INCOME FUND CLASS C
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1998
<PERIOD-START> FEB-01-1997
<PERIOD-END> JUL-31-1997
<INVESTMENTS-AT-COST> 1028795832
<INVESTMENTS-AT-VALUE> 1068792355
<RECEIVABLES> 63761535
<ASSETS-OTHER> 8714
<OTHER-ITEMS-ASSETS> 4952
<TOTAL-ASSETS> 1132567556
<PAYABLE-FOR-SECURITIES> 36573443
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 11678262
<TOTAL-LIABILITIES> 48251705
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1300371257
<SHARES-COMMON-STOCK> 7530183
<SHARES-COMMON-PRIOR> 5265960
<ACCUMULATED-NII-CURRENT> 2098105
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (258150034)
<ACCUM-APPREC-OR-DEPREC> 39996523
<NET-ASSETS> 1084315851
<DIVIDEND-INCOME> 1512918
<INTEREST-INCOME> 48116048
<OTHER-INCOME> 0
<EXPENSES-NET> (6224107)
<NET-INVESTMENT-INCOME> 43404859
<REALIZED-GAINS-CURRENT> 15956458
<APPREC-INCREASE-CURRENT> 14461469
<NET-CHANGE-FROM-OPS> 73822786
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (1286355)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 3936249
<NUMBER-OF-SHARES-REDEEMED> (1801656)
<SHARES-REINVESTED> 129630
<NET-CHANGE-IN-ASSETS> 80018493
<ACCUMULATED-NII-PRIOR> 1677232
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> (274106492)
<GROSS-ADVISORY-FEES> 2302327
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 6577525
<AVERAGE-NET-ASSETS> 1013654560
<PER-SHARE-NAV-BEGIN> 5.36
<PER-SHARE-NII> 0.25
<PER-SHARE-GAIN-APPREC> 0.11
<PER-SHARE-DIVIDEND> (0.21)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 5.51
<EXPENSE-RATIO> 1.73
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 014
<NAME> MFS HIGH INCOME FUND CLASS I
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1998
<PERIOD-START> FEB-01-1997
<PERIOD-END> JUL-31-1997
<INVESTMENTS-AT-COST> 1028795832
<INVESTMENTS-AT-VALUE> 1068792355
<RECEIVABLES> 63761535
<ASSETS-OTHER> 8714
<OTHER-ITEMS-ASSETS> 4952
<TOTAL-ASSETS> 1132567556
<PAYABLE-FOR-SECURITIES> 36573443
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 11678262
<TOTAL-LIABILITIES> 48251705
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1300371257
<SHARES-COMMON-STOCK> 635537
<SHARES-COMMON-PRIOR> 572355
<ACCUMULATED-NII-CURRENT> 2098105
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (258150034)
<ACCUM-APPREC-OR-DEPREC> 39996523
<NET-ASSETS> 1084315851
<DIVIDEND-INCOME> 1512918
<INTEREST-INCOME> 48116048
<OTHER-INCOME> 0
<EXPENSES-NET> (6224107)
<NET-INVESTMENT-INCOME> 43404859
<REALIZED-GAINS-CURRENT> 15956458
<APPREC-INCREASE-CURRENT> 14461469
<NET-CHANGE-FROM-OPS> 73822786
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (143893)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 41168
<NUMBER-OF-SHARES-REDEEMED> (4798)
<SHARES-REINVESTED> 26812
<NET-CHANGE-IN-ASSETS> 80018493
<ACCUMULATED-NII-PRIOR> 1677232
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> (274106492)
<GROSS-ADVISORY-FEES> 2302327
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 6577525
<AVERAGE-NET-ASSETS> 1013654560
<PER-SHARE-NAV-BEGIN> 5.35
<PER-SHARE-NII> 0.24
<PER-SHARE-GAIN-APPREC> 0.19
<PER-SHARE-DIVIDEND> (0.28)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 5.50
<EXPENSE-RATIO> 0.73
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 021
<NAME> MUNICIPAL HIGH INCOME FUND CLASS A
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1998
<PERIOD-START> FEB-01-1997
<PERIOD-END> JUL-31-1997
<INVESTMENTS-AT-COST> 1127806104
<INVESTMENTS-AT-VALUE> 1223353211
<RECEIVABLES> 30879485
<ASSETS-OTHER> 9760
<OTHER-ITEMS-ASSETS> 44576
<TOTAL-ASSETS> 1254287032
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 9132771
<TOTAL-LIABILITIES> 9132771
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1305354137
<SHARES-COMMON-STOCK> 118658090
<SHARES-COMMON-PRIOR> 113048629
<ACCUMULATED-NII-CURRENT> 427555
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (156174538)
<ACCUM-APPREC-OR-DEPREC> 95547107
<NET-ASSETS> 1245154261
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 43643369
<OTHER-INCOME> 0
<EXPENSES-NET> 5668111
<NET-INVESTMENT-INCOME> 37975258
<REALIZED-GAINS-CURRENT> (24415973)
<APPREC-INCREASE-CURRENT> 48115127
<NET-CHANGE-FROM-OPS> 61714412
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (33714468)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 13001707
<NUMBER-OF-SHARES-REDEEMED> (8915500)
<SHARES-REINVESTED> 1423254
<NET-CHANGE-IN-ASSETS> 131005744
<ACCUMULATED-NII-PRIOR> 618295
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> (131758565)
<GROSS-ADVISORY-FEES> 3787054
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 5825987
<AVERAGE-NET-ASSETS> 1147456880
<PER-SHARE-NAV-BEGIN> 8.73
<PER-SHARE-NII> 0.29
<PER-SHARE-GAIN-APPREC> 0.17
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> (0.29)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 8.90
<EXPENSE-RATIO> 0.88
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 022
<NAME> MUNICIPAL HIGH INCOME FUND CLASS B
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1998
<PERIOD-START> FEB-01-1997
<PERIOD-END> JUL-31-1997
<INVESTMENTS-AT-COST> 1127806104
<INVESTMENTS-AT-VALUE> 1223353211
<RECEIVABLES> 30879485
<ASSETS-OTHER> 9760
<OTHER-ITEMS-ASSETS> 44576
<TOTAL-ASSETS> 1254287032
<PAYABLE-FOR-SECURITIES> 0
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 9132771
<TOTAL-LIABILITIES> 9132771
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1305354137
<SHARES-COMMON-STOCK> 21244347
<SHARES-COMMON-PRIOR> 14411582
<ACCUMULATED-NII-CURRENT> 427555
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (156174538)
<ACCUM-APPREC-OR-DEPREC> 95547107
<NET-ASSETS> 1245154261
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 43643369
<OTHER-INCOME> 0
<EXPENSES-NET> 5668111
<NET-INVESTMENT-INCOME> 37975258
<REALIZED-GAINS-CURRENT> (24415973)
<APPREC-INCREASE-CURRENT> 48115127
<NET-CHANGE-FROM-OPS> 61714412
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (33714468)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 7707439
<NUMBER-OF-SHARES-REDEEMED> (1045681)
<SHARES-REINVESTED> 171007
<NET-CHANGE-IN-ASSETS> 131005744
<ACCUMULATED-NII-PRIOR> 618295
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> (131758565)
<GROSS-ADVISORY-FEES> 3787054
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 5825987
<AVERAGE-NET-ASSETS> 1147456880
<PER-SHARE-NAV-BEGIN> 8.74
<PER-SHARE-NII> 0.25
<PER-SHARE-GAIN-APPREC> 0.18
<PER-SHARE-DIVIDEND> 0
<PER-SHARE-DISTRIBUTIONS> (0.26)
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 8.91
<EXPENSE-RATIO> 1.73
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>