<PAGE> PAGE 1
000 A000000 07/31/98
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 3
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 C020300 MFS HIGH YIELD OPPORTUNITIES FUND
007 C030300 N
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
<PAGE> PAGE 2
011 C01AA01 BOSTON
011 C02AA01 MA
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 59
019 C00AA00 MASSFINSER
020 A000001 MERRILL LYNCH
020 B000001 13-5674085
020 C000001 4
020 A000002 GOLDMAN SACHS & CO.
020 B000002 13-5108880
020 C000002 2
020 C000003 0
020 C000004 0
020 C000005 0
020 C000006 0
020 C000007 0
020 C000008 0
020 C000009 0
020 C000010 0
021 000000 6
022 A000001 GENERAL ELECTRIC CAP CORP.
022 B000001 00-0000000
022 C000001 436965
022 D000001 0
022 A000002 GENERAL ELECTRIC CO.
022 B000002 00-0000000
022 C000002 263438
022 D000002 4988
022 A000003 MERRILL LYNCH
022 B000003 13-5674085
022 C000003 174339
022 D000003 78115
022 A000004 DLJ FIXED INCOME
022 B000004 13-2741729
022 C000004 124923
022 D000004 63824
022 A000005 PRUDENTIAL SECURITIES
022 B000005 22-2347336
022 C000005 125888
022 D000005 57540
022 A000006 MORGAN (J.P.) SECURITIES
022 B000006 13-3224016
022 C000006 97443
022 D000006 54165
<PAGE> PAGE 3
022 A000007 BEAR STEARNS & CO, INC.
022 B000007 13-3299429
022 C000007 95133
022 D000007 44693
022 A000008 MORGAN STANLEY
022 B000008 13-2655998
022 C000008 75172
022 D000008 48082
022 A000009 NATIONS BANK
022 B000009 75-0520130
022 C000009 106722
022 D000009 14093
022 A000010 GOLDMAN SACHS & CO.
022 B000010 13-5108880
022 C000010 78376
022 D000010 40337
023 C000000 2664272
023 D000000 1193963
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 Y
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 C000000 Y
077 H000000 Y
<PAGE> PAGE 4
077 Q010000 Y
078 000000 N
080 C00AA00 0
081 B00AA00 0
082 B00AA00 0
083 A00AA00 N
083 B00AA00 0
084 A00AA00 N
084 B00AA00 0
085 A00AA00 Y
085 B00AA00 N
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 MERRILL LYNCH INVESTORS,INC.
025 B000101 00-0000000
025 C000101 D
025 D000101 4361
025 D000102 0
<PAGE> PAGE 5
025 D000103 0
025 D000104 0
025 D000105 0
025 D000106 0
025 D000107 0
025 D000108 0
028 A010100 55606
028 A020100 4848
028 A030100 0
028 A040100 31835
028 B010100 68483
028 B020100 5615
028 B030100 0
028 B040100 50831
028 C010100 57611
028 C020100 4823
028 C030100 0
028 C040100 66803
028 D010100 64284
028 D020100 4859
028 D030100 0
028 D040100 41662
028 E010100 52054
028 E020100 4916
028 E030100 0
028 E040100 48690
028 F010100 79980
028 F020100 5098
028 F030100 0
028 F040100 31617
028 G010100 378018
028 G020100 30159
028 G030100 0
028 G040100 271438
028 H000100 152732
029 000100 Y
030 A000100 1552
030 B000100 4.75
030 C000100 0.00
031 A000100 275
031 B000100 0
032 000100 1277
033 000100 0
034 000100 Y
035 000100 374
036 A000100 N
036 B000100 0
037 000100 N
038 000100 0
039 000100 N
040 000100 Y
<PAGE> PAGE 6
041 000100 Y
042 A000100 0
042 B000100 0
042 C000100 49
042 D000100 51
042 E000100 0
042 F000100 0
042 G000100 0
042 H000100 0
043 000100 3634
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
<PAGE> PAGE 7
060 B000100 Y
061 000100 1000
062 A000100 Y
062 B000100 0.0
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 5.3
062 M000100 0.0
062 N000100 0.0
062 O000100 0.0
062 P000100 80.6
062 Q000100 8.0
062 R000100 4.2
063 A000100 0
063 B000100 8.3
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 Y
070 N010100 Y
<PAGE> PAGE 8
070 N020100 N
070 O010100 Y
070 O020100 N
070 P010100 Y
070 P020100 N
070 Q010100 N
070 Q020100 N
070 R010100 N
070 R020100 N
071 A000100 957248
071 B000100 881570
071 C000100 1231108
071 D000100 72
072 A000100 6
072 B000100 58583
072 C000100 865
072 D000100 0
072 E000100 0
072 F000100 2778
072 G000100 92
072 H000100 0
072 I000100 715
072 J000100 78
072 K000100 99
072 L000100 64
072 M000100 32
072 N000100 0
072 O000100 0
072 P000100 0
072 Q000100 0
072 R000100 26
072 S000100 4
072 T000100 3634
072 U000100 0
072 V000100 0
072 W000100 401
072 X000100 7923
072 Y000100 50
072 Z000100 51575
072AA000100 25007
072BB000100 0
072CC010100 0
072CC020100 21777
072DD010100 32216
072DD020100 16156
072EE000100 0
073 A010100 0.2300
073 A020100 0.2100
073 B000100 0.0000
073 C000100 0.0000
074 A000100 321
<PAGE> PAGE 9
074 B000100 0
074 C000100 71180
074 D000100 1205056
074 E000100 51527
074 F000100 133
074 G000100 0
074 H000100 0
074 I000100 0
074 J000100 17064
074 K000100 0
074 L000100 35171
074 M000100 8
074 N000100 1380460
074 O000100 20401
074 P000100 391
074 Q000100 0
074 R010100 0
074 R020100 0
074 R030100 0
074 R040100 4860
074 S000100 0
074 T000100 1354808
074 U010100 140527
074 U020100 83915
074 V010100 5.64
074 V020100 5.64
074 W000100 0.0000
074 X000100 61069
074 Y000100 0
075 A000100 0
075 B000100 1278621
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
<PAGE> PAGE 10
015 C020203 NY
015 C030203 10041
015 E010203 X
015 A000204 MORGAN GUARANTY TRUST COMPANY
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 A000201 DELETE
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 24856
028 A020200 2317
028 A030200 0
028 A040200 13211
028 B010200 26999
028 B020200 2326
028 B030200 0
028 B040200 20306
028 C010200 25945
028 C020200 2315
028 C030200 0
028 C040200 22478
028 D010200 30495
028 D020200 2342
028 D030200 0
028 D040200 14211
028 E010200 32546
028 E020200 2379
028 E030200 0
028 E040200 16467
028 F010200 45188
028 F020200 2458
028 F030200 0
028 F040200 24132
028 G010200 186029
028 G020200 14137
<PAGE> PAGE 11
028 G030200 0
028 G040200 110805
028 H000200 119359
029 000200 Y
030 A000200 2525
030 B000200 4.75
030 C000200 0.00
031 A000200 458
031 B000200 0
032 000200 2067
033 000200 0
034 000200 Y
035 000200 442
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 85
042 D000200 15
042 E000200 0
042 F000200 0
042 G000200 0
042 H000200 0
043 000200 1260
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
<PAGE> PAGE 12
048 I020200 0.000
048 J010200 0
048 J020200 0.000
048 K010200 0
048 K020200 0.000
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 1.5
062 M000200 0.0
062 N000200 0.0
062 O000200 98.5
062 P000200 0.0
062 Q000200 0.0
062 R000200 0.0
063 A000200 0
063 B000200 22.6
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
<PAGE> PAGE 13
070 D020200 N
070 E010200 Y
070 E020200 N
070 F010200 N
070 F020200 N
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 146235
071 B000200 52396
071 C000200 1375042
071 D000200 4
072 A000200 6
072 B000200 46716
072 C000200 0
072 D000200 0
072 E000200 0
072 F000200 4292
072 G000200 99
072 H000200 0
072 I000200 782
072 J000200 169
072 K000200 52
072 L000200 47
072 M000200 40
072 N000200 0
072 O000200 0
072 P000200 0
072 Q000200 0
072 R000200 21
<PAGE> PAGE 14
072 S000200 20
072 T000200 1260
072 U000200 0
072 V000200 0
072 W000200 302
072 X000200 7084
072 Y000200 150
072 Z000200 39782
072AA000200 0
072BB000200 417
072CC010200 0
072CC020200 13165
072DD010200 32562
072DD020200 7112
072EE000200 0
073 A010200 0.2600
073 A020200 0.2200
073 B000200 0.0000
073 C000200 0.0000
074 A000200 18
074 B000200 0
074 C000200 21600
074 D000200 1426228
074 E000200 0
074 F000200 0
074 G000200 0
074 H000200 0
074 I000200 0
074 J000200 4027
074 K000200 0
074 L000200 25726
074 M000200 8
074 N000200 1477607
074 O000200 16283
074 P000200 164
074 Q000200 0
074 R010200 0
074 R020200 0
074 R030200 0
074 R040200 13516
074 S000200 0
074 T000200 1447644
074 U010200 126214
074 U020200 34853
074 V010200 8.99
074 V020200 8.99
074 W000200 0.0000
074 X000200 32247
074 Y000200 0
075 A000200 0
075 B000200 1397712
<PAGE> PAGE 15
076 000200 0.00
013 A000301 DELOITTE & TOUCHE LLP
013 B010301 BOSTON
013 B020301 MA
013 B030301 02110
015 A000301 STATE STREET BANK AND TRUST COMPANY
015 B000301 C
015 C010301 BOSTON
015 C020301 MA
015 C030301 02110
015 E010301 X
015 A000302 THE BANK OF NEW YORK
015 B000302 S
015 C010302 NEW YORK
015 C020302 NY
015 C030302 10286
015 E010302 X
024 000300 N
025 D000301 0
025 D000302 0
025 D000303 0
025 D000304 0
025 D000305 0
025 D000306 0
025 D000307 0
025 D000308 0
028 A010300 0
028 A020300 0
028 A030300 0
028 A040300 0
028 B010300 0
028 B020300 0
028 B030300 0
028 B040300 0
028 C010300 0
028 C020300 0
028 C030300 0
028 C040300 0
028 D010300 0
028 D020300 0
028 D030300 0
028 D040300 0
028 E010300 0
028 E020300 0
028 E030300 0
028 E040300 0
028 F010300 2553
028 F020300 10
028 F030300 0
028 F040300 0
028 G010300 2553
<PAGE> PAGE 16
028 G020300 10
028 G030300 0
028 G040300 0
028 H000300 1762
029 000300 Y
030 A000300 4
030 B000300 4.75
030 C000300 0.00
031 A000300 1
031 B000300 0
032 000300 3
033 000300 0
034 000300 Y
035 000300 0
036 A000300 N
036 B000300 0
037 000300 N
038 000300 0
039 000300 N
040 000300 Y
041 000300 Y
042 A000300 0
042 B000300 0
042 C000300 40
042 D000300 60
042 E000300 0
042 F000300 0
042 G000300 0
042 H000300 0
043 000300 535
044 000300 0
045 000300 Y
046 000300 N
047 000300 Y
048 000300 0.650
048 A010300 0
048 A020300 0.000
048 B010300 0
048 B020300 0.000
048 C010300 0
048 C020300 0.000
048 D010300 0
048 D020300 0.000
048 E010300 0
048 E020300 0.000
048 F010300 0
048 F020300 0.000
048 G010300 0
048 G020300 0.000
048 H010300 0
048 H020300 0.000
<PAGE> PAGE 17
048 I010300 0
048 I020300 0.000
048 J010300 0
048 J020300 0.000
048 K010300 0
048 K020300 0.000
049 000300 N
050 000300 N
051 000300 N
052 000300 N
053 A000300 Y
053 B000300 N
053 C000300 Y
055 A000300 Y
055 B000300 N
056 000300 Y
057 000300 N
058 A000300 N
059 000300 Y
060 A000300 Y
060 B000300 Y
061 000300 1000
062 A000300 Y
062 B000300 0.0
062 C000300 0.0
062 D000300 0.0
062 E000300 0.0
062 F000300 0.0
062 G000300 0.0
062 H000300 0.0
062 I000300 0.0
062 J000300 0.0
062 K000300 0.0
062 L000300 0.0
062 M000300 0.0
062 N000300 0.0
062 O000300 0.0
062 P000300 69.4
062 Q000300 26.6
062 R000300 1.0
063 A000300 0
063 B000300 0.0
064 A000300 N
064 B000300 N
070 A010300 Y
070 A020300 N
070 B010300 N
070 B020300 N
070 C010300 Y
070 C020300 N
070 D010300 N
<PAGE> PAGE 18
070 D020300 N
070 E010300 Y
070 E020300 N
070 F010300 N
070 F020300 N
070 G010300 Y
070 G020300 N
070 H010300 N
070 H020300 N
070 I010300 N
070 I020300 N
070 J010300 Y
070 J020300 Y
070 K010300 Y
070 K020300 N
070 L010300 Y
070 L020300 Y
070 M010300 Y
070 M020300 N
070 N010300 Y
070 N020300 N
070 O010300 Y
070 O020300 N
070 P010300 Y
070 P020300 N
070 Q010300 N
070 Q020300 N
070 R010300 N
070 R020300 N
071 A000300 3177
071 B000300 691
071 C000300 2472
071 D000300 28
072 A000300 6
072 B000300 13
072 C000300 0
072 D000300 0
072 E000300 0
072 F000300 0
072 G000300 0
072 H000300 0
072 I000300 0
072 J000300 0
072 K000300 0
072 L000300 4
072 M000300 0
072 N000300 45
072 O000300 0
072 P000300 0
072 Q000300 0
072 R000300 16
<PAGE> PAGE 19
072 S000300 0
072 T000300 0
072 U000300 0
072 V000300 0
072 W000300 4
072 X000300 69
072 Y000300 67
072 Z000300 11
072AA000300 7
072BB000300 0
072CC010300 0
072CC020300 23
072DD010300 10
072DD020300 2
072EE000300 0
073 A010300 0.0700
073 A020300 0.0600
073 B000300 0.0000
073 C000300 0.0000
074 A000300 0
074 B000300 0
074 C000300 0
074 D000300 2447
074 E000300 0
074 F000300 25
074 G000300 0
074 H000300 0
074 I000300 0
074 J000300 319
074 K000300 0
074 L000300 155
074 M000300 0
074 N000300 2946
074 O000300 298
074 P000300 0
074 Q000300 0
074 R010300 0
074 R020300 0
074 R030300 0
074 R040300 101
074 S000300 0
074 T000300 2547
074 U010300 177
074 U020300 72
074 V010300 9.95
074 V020300 9.94
074 W000300 0.0000
074 X000300 139
074 Y000300 0
075 A000300 0
075 B000300 1520
<PAGE> PAGE 20
076 000300 0.00
SIGNATURE ELLEN MOYNIHAN
TITLE ASSISTANT TREASURER
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 031
<NAME> MFS HIGH YIELD OPPORTUNITIES FUND CLASS A
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1999
<PERIOD-START> JUL-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 2495075
<INVESTMENTS-AT-VALUE> 2471617
<RECEIVABLES> 474387
<ASSETS-OTHER> 11
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 2946015
<PAYABLE-FOR-SECURITIES> 297945
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 100650
<TOTAL-LIABILITIES> 398595
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 2563786
<SHARES-COMMON-STOCK> 176931
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (376)
<ACCUMULATED-NET-GAINS> 7459
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (23449)
<NET-ASSETS> 2547420
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 12782
<OTHER-INCOME> 0
<EXPENSES-NET> (1348)
<NET-INVESTMENT-INCOME> 11434
<REALIZED-GAINS-CURRENT> 7459
<APPREC-INCREASE-CURRENT> (23449)
<NET-CHANGE-FROM-OPS> (4556)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (10150)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 175923
<NUMBER-OF-SHARES-REDEEMED> (0)
<SHARES-REINVESTED> 1008
<NET-CHANGE-IN-ASSETS> 2547420
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> (0)
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 812
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 68752
<AVERAGE-NET-ASSETS> 1520104
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> 0.07
<PER-SHARE-GAIN-APPREC> (0.05)
<PER-SHARE-DIVIDEND> (0.07)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 9.95
<EXPENSE-RATIO> 1.00
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 032
<NAME> MFS HIGH YIELD OPPORTUNITIES FUND CLASS B
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1999
<PERIOD-START> JUL-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 2495075
<INVESTMENTS-AT-VALUE> 2471617
<RECEIVABLES> 474387
<ASSETS-OTHER> 11
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 2946015
<PAYABLE-FOR-SECURITIES> 297945
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 100650
<TOTAL-LIABILITIES> 398595
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 2563786
<SHARES-COMMON-STOCK> 71612
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (376)
<ACCUMULATED-NET-GAINS> 7459
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (23449)
<NET-ASSETS> 2547420
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 12782
<OTHER-INCOME> 0
<EXPENSES-NET> (1348)
<NET-INVESTMENT-INCOME> 11434
<REALIZED-GAINS-CURRENT> 7459
<APPREC-INCREASE-CURRENT> (23449)
<NET-CHANGE-FROM-OPS> (4556)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (1601)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 71575
<NUMBER-OF-SHARES-REDEEMED> (0)
<SHARES-REINVESTED> 37
<NET-CHANGE-IN-ASSETS> 2547420
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> (0)
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 812
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 68752
<AVERAGE-NET-ASSETS> 1520104
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> 0.04
<PER-SHARE-GAIN-APPREC> (0.04)
<PER-SHARE-DIVIDEND> (0.06)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 9.94
<EXPENSE-RATIO> 1.65
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 033
<NAME> MFS HIGH YIELD OPPORTUNITIES FUND CLASS C
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1999
<PERIOD-START> JUL-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 2495075
<INVESTMENTS-AT-VALUE> 2471617
<RECEIVABLES> 474387
<ASSETS-OTHER> 11
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 2946015
<PAYABLE-FOR-SECURITIES> 297945
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 100650
<TOTAL-LIABILITIES> 398595
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 2563786
<SHARES-COMMON-STOCK> 7491
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (376)
<ACCUMULATED-NET-GAINS> 7459
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (23449)
<NET-ASSETS> 2547420
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 12782
<OTHER-INCOME> 0
<EXPENSES-NET> (1348)
<NET-INVESTMENT-INCOME> 11434
<REALIZED-GAINS-CURRENT> 7459
<APPREC-INCREASE-CURRENT> (23449)
<NET-CHANGE-FROM-OPS> (4556)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (58)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 7490
<NUMBER-OF-SHARES-REDEEMED> (1)
<SHARES-REINVESTED> 2
<NET-CHANGE-IN-ASSETS> 2547420
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> (0)
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 812
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 68752
<AVERAGE-NET-ASSETS> 1520104
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> 0.01
<PER-SHARE-GAIN-APPREC> 0.00
<PER-SHARE-DIVIDEND> (0.06)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 9.95
<EXPENSE-RATIO> 1.65
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<TABLE> <S> <C>
<ARTICLE> 6
<CIK> 0000225604
<NAME> MFS SERIES TRUST III
<SERIES>
<NUMBER> 034
<NAME> MFS HIGH YIELD OPPORTUNITIES FUND CLASS I
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1999
<PERIOD-START> JUL-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 2495075
<INVESTMENTS-AT-VALUE> 2471617
<RECEIVABLES> 474387
<ASSETS-OTHER> 11
<OTHER-ITEMS-ASSETS> 0
<TOTAL-ASSETS> 2946015
<PAYABLE-FOR-SECURITIES> 297945
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 100650
<TOTAL-LIABILITIES> 398595
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 2563786
<SHARES-COMMON-STOCK> 16
<SHARES-COMMON-PRIOR> 0
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (376)
<ACCUMULATED-NET-GAINS> 7459
<OVERDISTRIBUTION-GAINS> 0
<ACCUM-APPREC-OR-DEPREC> (23449)
<NET-ASSETS> 2547420
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 12782
<OTHER-INCOME> 0
<EXPENSES-NET> (1348)
<NET-INVESTMENT-INCOME> 11434
<REALIZED-GAINS-CURRENT> 7459
<APPREC-INCREASE-CURRENT> (23449)
<NET-CHANGE-FROM-OPS> (4556)
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (1)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 15
<NUMBER-OF-SHARES-REDEEMED> (0)
<SHARES-REINVESTED> 1
<NET-CHANGE-IN-ASSETS> 2547420
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> (0)
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 812
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 68752
<AVERAGE-NET-ASSETS> 1520104
<PER-SHARE-NAV-BEGIN> 10.00
<PER-SHARE-NII> 0.50
<PER-SHARE-GAIN-APPREC> (0.48)
<PER-SHARE-DIVIDEND> (0.07)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 9.95
<EXPENSE-RATIO> 0.65
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>
<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-31-1999
<PERIOD-START> FEB-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 1309042653
<INVESTMENTS-AT-VALUE> 1327896504
<RECEIVABLES> 52234934
<ASSETS-OTHER> 7569
<OTHER-ITEMS-ASSETS> 321249
<TOTAL-ASSETS> 1380460256
<PAYABLE-FOR-SECURITIES> 20400917
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 5251755
<TOTAL-LIABILITIES> 25652672
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1542506080
<SHARES-COMMON-STOCK> 140526548
<SHARES-COMMON-PRIOR> 136325997
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (2388472)
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (204182456)
<ACCUM-APPREC-OR-DEPREC> 18872432
<NET-ASSETS> 1354807584
<DIVIDEND-INCOME> 865376
<INTEREST-INCOME> 58582659
<OTHER-INCOME> 0
<EXPENSES-NET> (7873131)
<NET-INVESTMENT-INCOME> 51574904
<REALIZED-GAINS-CURRENT> 25007408
<APPREC-INCREASE-CURRENT> (21777083)
<NET-CHANGE-FROM-OPS> 54805229
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (32216224)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 26995780
<NUMBER-OF-SHARES-REDEEMED> (26182252)
<SHARES-REINVESTED> 3387023
<NET-CHANGE-IN-ASSETS> 139687249
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> (229189864)
<OVERDISTRIB-NII-PRIOR> (2800915)
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 2778209
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 7923276
<AVERAGE-NET-ASSETS> 1278620729
<PER-SHARE-NAV-BEGIN> 5.62
<PER-SHARE-NII> 0.24
<PER-SHARE-GAIN-APPREC> .01
<PER-SHARE-DIVIDEND> (0.23)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 5.64
<EXPENSE-RATIO> 0.98
<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-31-1999
<PERIOD-START> FEB-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 1309042653
<INVESTMENTS-AT-VALUE> 1327896504
<RECEIVABLES> 52234934
<ASSETS-OTHER> 7569
<OTHER-ITEMS-ASSETS> 321249
<TOTAL-ASSETS> 1380460256
<PAYABLE-FOR-SECURITIES> 20400917
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 5251755
<TOTAL-LIABILITIES> 25652672
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1542506080
<SHARES-COMMON-STOCK> 83915271
<SHARES-COMMON-PRIOR> 68598280
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (2388472)
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (204182456)
<ACCUM-APPREC-OR-DEPREC> 18872432
<NET-ASSETS> 1354807584
<DIVIDEND-INCOME> 865376
<INTEREST-INCOME> 58582659
<OTHER-INCOME> 0
<EXPENSES-NET> (7873131)
<NET-INVESTMENT-INCOME> 51574904
<REALIZED-GAINS-CURRENT> 25007408
<APPREC-INCREASE-CURRENT> (21777083)
<NET-CHANGE-FROM-OPS> 54805229
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (16156146)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 30082792
<NUMBER-OF-SHARES-REDEEMED> (16308231)
<SHARES-REINVESTED> 1542430
<NET-CHANGE-IN-ASSETS> 139687249
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> (229189864)
<OVERDISTRIB-NII-PRIOR> (2800915)
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 2778209
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 7923276
<AVERAGE-NET-ASSETS> 1278620729
<PER-SHARE-NAV-BEGIN> 5.62
<PER-SHARE-NII> 0.22
<PER-SHARE-GAIN-APPREC> .01
<PER-SHARE-DIVIDEND> (0.21)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 5.64
<EXPENSE-RATIO> 1.68
<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-31-1999
<PERIOD-START> FEB-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 1309042653
<INVESTMENTS-AT-VALUE> 1327896504
<RECEIVABLES> 52234934
<ASSETS-OTHER> 7569
<OTHER-ITEMS-ASSETS> 321249
<TOTAL-ASSETS> 1380460256
<PAYABLE-FOR-SECURITIES> 20400917
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 5251755
<TOTAL-LIABILITIES> 25652672
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1542506080
<SHARES-COMMON-STOCK> 14255216
<SHARES-COMMON-PRIOR> 10679900
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (2388472)
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (204182456)
<ACCUM-APPREC-OR-DEPREC> 18872432
<NET-ASSETS> 1354807584
<DIVIDEND-INCOME> 865376
<INTEREST-INCOME> 58582659
<OTHER-INCOME> 0
<EXPENSES-NET> (7873131)
<NET-INVESTMENT-INCOME> 51574904
<REALIZED-GAINS-CURRENT> 25007408
<APPREC-INCREASE-CURRENT> (21777083)
<NET-CHANGE-FROM-OPS> 54805229
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (2602892)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 8809773
<NUMBER-OF-SHARES-REDEEMED> (5607673)
<SHARES-REINVESTED> 373216
<NET-CHANGE-IN-ASSETS> 139687249
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> (229189864)
<OVERDISTRIB-NII-PRIOR> (2800915)
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 2778209
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 7923276
<AVERAGE-NET-ASSETS> 1278620729
<PER-SHARE-NAV-BEGIN> 5.64
<PER-SHARE-NII> 0.22
<PER-SHARE-GAIN-APPREC> .00
<PER-SHARE-DIVIDEND> (0.21)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 5.65
<EXPENSE-RATIO> 1.68
<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-31-1999
<PERIOD-START> FEB-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 1309042653
<INVESTMENTS-AT-VALUE> 1327896504
<RECEIVABLES> 52234934
<ASSETS-OTHER> 7569
<OTHER-ITEMS-ASSETS> 321249
<TOTAL-ASSETS> 1380460256
<PAYABLE-FOR-SECURITIES> 20400917
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 5251755
<TOTAL-LIABILITIES> 25652672
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1542506080
<SHARES-COMMON-STOCK> 1569183
<SHARES-COMMON-PRIOR> 642700
<ACCUMULATED-NII-CURRENT> 0
<OVERDISTRIBUTION-NII> (2388472)
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (204182456)
<ACCUM-APPREC-OR-DEPREC> 18872432
<NET-ASSETS> 1354807584
<DIVIDEND-INCOME> 865376
<INTEREST-INCOME> 58582659
<OTHER-INCOME> 0
<EXPENSES-NET> (7873131)
<NET-INVESTMENT-INCOME> 51574904
<REALIZED-GAINS-CURRENT> 25007408
<APPREC-INCREASE-CURRENT> (21777083)
<NET-CHANGE-FROM-OPS> 54805229
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (187199)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 915235
<NUMBER-OF-SHARES-REDEEMED> (21915)
<SHARES-REINVESTED> 33163
<NET-CHANGE-IN-ASSETS> 139687249
<ACCUMULATED-NII-PRIOR> 0
<ACCUMULATED-GAINS-PRIOR> (229189864)
<OVERDISTRIB-NII-PRIOR> (2800915)
<OVERDIST-NET-GAINS-PRIOR> 0
<GROSS-ADVISORY-FEES> 2778209
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 7923276
<AVERAGE-NET-ASSETS> 1278620729
<PER-SHARE-NAV-BEGIN> 5.61
<PER-SHARE-NII> 0.24
<PER-SHARE-GAIN-APPREC> .02
<PER-SHARE-DIVIDEND> (0.24)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 5.63
<EXPENSE-RATIO> 0.69
<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> MFS MUNICIPAL HIGH INCOME FUND CLASS A
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1999
<PERIOD-START> FEB-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 1319684953
<INVESTMENTS-AT-VALUE> 1447827520
<RECEIVABLES> 29752864
<ASSETS-OTHER> 8794
<OTHER-ITEMS-ASSETS> 17564
<TOTAL-ASSETS> 1477606742
<PAYABLE-FOR-SECURITIES> 16282577
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 13680456
<TOTAL-LIABILITIES> 29963033
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1493756973
<SHARES-COMMON-STOCK> 126214400
<SHARES-COMMON-PRIOR> 122019211
<ACCUMULATED-NII-CURRENT> 641929
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (174897760)
<ACCUM-APPREC-OR-DEPREC> 128142567
<NET-ASSETS> 1447643709
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 46716142
<OTHER-INCOME> 0
<EXPENSES-NET> 6934328
<NET-INVESTMENT-INCOME> 39781814
<REALIZED-GAINS-CURRENT> (417158)
<APPREC-INCREASE-CURRENT> (13164988)
<NET-CHANGE-FROM-OPS> 26199668
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (32561937)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 13256336
<NUMBER-OF-SHARES-REDEEMED> (10378457)
<SHARES-REINVESTED> 1317310
<NET-CHANGE-IN-ASSETS> 75888083
<ACCUMULATED-NII-PRIOR> 534220
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> (174480602)
<GROSS-ADVISORY-FEES> 4291868
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 7083921
<AVERAGE-NET-ASSETS> 1397712365
<PER-SHARE-NAV-BEGIN> 9.07
<PER-SHARE-NII> 0.26
<PER-SHARE-GAIN-APPREC> (0.08)
<PER-SHARE-DIVIDEND> (0.26)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 8.99
<EXPENSE-RATIO> 0.84
<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> MFS MUNICIPAL HIGH INCOME FUND CLASS B
<MULTIPLIER> 1
<S> <C>
<PERIOD-TYPE> 6-MOS
<FISCAL-YEAR-END> JAN-31-1999
<PERIOD-START> FEB-01-1998
<PERIOD-END> JUL-31-1998
<INVESTMENTS-AT-COST> 1319684953
<INVESTMENTS-AT-VALUE> 1447827520
<RECEIVABLES> 29752864
<ASSETS-OTHER> 8794
<OTHER-ITEMS-ASSETS> 17564
<TOTAL-ASSETS> 1477606742
<PAYABLE-FOR-SECURITIES> 16282577
<SENIOR-LONG-TERM-DEBT> 0
<OTHER-ITEMS-LIABILITIES> 13680456
<TOTAL-LIABILITIES> 29963033
<SENIOR-EQUITY> 0
<PAID-IN-CAPITAL-COMMON> 1493756973
<SHARES-COMMON-STOCK> 34853487
<SHARES-COMMON-PRIOR> 29132515
<ACCUMULATED-NII-CURRENT> 641929
<OVERDISTRIBUTION-NII> 0
<ACCUMULATED-NET-GAINS> 0
<OVERDISTRIBUTION-GAINS> (174897760)
<ACCUM-APPREC-OR-DEPREC> 128142567
<NET-ASSETS> 1447643709
<DIVIDEND-INCOME> 0
<INTEREST-INCOME> 46716142
<OTHER-INCOME> 0
<EXPENSES-NET> 6934328
<NET-INVESTMENT-INCOME> 39781814
<REALIZED-GAINS-CURRENT> (417158)
<APPREC-INCREASE-CURRENT> (13164988)
<NET-CHANGE-FROM-OPS> 26199668
<EQUALIZATION> 0
<DISTRIBUTIONS-OF-INCOME> (7112168)
<DISTRIBUTIONS-OF-GAINS> 0
<DISTRIBUTIONS-OTHER> 0
<NUMBER-OF-SHARES-SOLD> 7394910
<NUMBER-OF-SHARES-REDEEMED> (1926914)
<SHARES-REINVESTED> 252976
<NET-CHANGE-IN-ASSETS> 75888083
<ACCUMULATED-NII-PRIOR> 534220
<ACCUMULATED-GAINS-PRIOR> 0
<OVERDISTRIB-NII-PRIOR> 0
<OVERDIST-NET-GAINS-PRIOR> (174480602)
<GROSS-ADVISORY-FEES> 4291868
<INTEREST-EXPENSE> 0
<GROSS-EXPENSE> 7083921
<AVERAGE-NET-ASSETS> 1397712365
<PER-SHARE-NAV-BEGIN> 9.08
<PER-SHARE-NII> 0.22
<PER-SHARE-GAIN-APPREC> (0.09)
<PER-SHARE-DIVIDEND> (0.22)
<PER-SHARE-DISTRIBUTIONS> 0
<RETURNS-OF-CAPITAL> 0
<PER-SHARE-NAV-END> 8.99
<EXPENSE-RATIO> 1.72
<AVG-DEBT-OUTSTANDING> 0
<AVG-DEBT-PER-SHARE> 0
</TABLE>