PAGE 1
000 B000000 12/31/2005
000 C000000 0000275694
000 D000000 N
000 E000000 NF
000 F000000 Y
000 G000000 N
000 H000000 N
000 I000000 6.1
000 J000000 A
001 A000000 MASSMUTUAL CORPORATE INVESTORS
001 B000000 811-2183
001 C000000 4132261000
002 A000000 1500 MAIN STREET, SUITE 600
002 B000000 SPRINGFIELD
002 C000000 MA
002 D010000 01115
002 D020000 0001
003 000000 N
004 000000 N
005 000000 N
006 000000 N
007 A000000 N
007 B000000 0
007 C010100 1
007 C010200 2
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 A000001 BABSON CAPITAL MANAGEMENT LLC
008 B000001 A
008 C000001 801-241
008 D010001 SPRINGFIELD
008 D020001 MA
008 D030001 01115
008 D040001 0001
012 A000001 SHAREHOLDER FINANCIAL SERVICES, INC.
012 B000001 84-1817
012 C010001 DENVER
012 C020001 CO
012 C030001 80217
012 C040001 3673
013 A000001 KPMG LLP
013 B010001 BOSTON
013 B020001 MA
013 B030001 02110
013 B040001 2371
PAGE 2
015 A000001 CITIBANK, N.A.
015 B000001 C
015 C010001 NEW YORK
015 C020001 NY
015 C030001 10043
015 E010001 X
018 000000 Y
019 A000000 Y
019 B000000 2
019 C000000 CIPIINVEST
020 A000001 LAZARD FRERES AND CO
020 B000001 13-5545100
020 C000001 5
020 A000002 ALLEN & CO
020 B000002 13-4132953
020 C000002 4
020 A000003 GOLDMAN, SACHS & CO
020 B000003 13-5108880
020 C000003 1
020 A000004 MERRILL, LYNCH ET AL
020 B000004 13-5674085
020 C000004 1
020 A000005 FIRST BOSTON CORP
020 B000005 13-5659485
020 C000005 1
020 A000006 SOUTHCOAST CAPITAL CORP
020 B000006 72-1164960
020 C000006 0
020 A000007 SALOMON SMITH BARNEY HOLD INC
020 B000007 11-2418191
020 C000007 0
020 A000008 STATE STREET BANK
020 B000008 13-4994650
020 C000008 0
020 A000009 J.P. MORGAN
020 B000009 13-4994650
020 C000009 0
020 A000010 SPEAR LEADS MFN
020 B000010 13-5515460
020 C000010 0
021 000000 14
022 A000001 JP MORGAN CHASE
022 B000001 13-4994650
022 C000001 228736
022 D000001 7840
022 A000002 GOLDMAN, SACHS & CO
022 B000002 13-5108880
022 C000002 157541
022 D000002 4364
022 A000003 MERRILL, LYNCH ET AL
022 B000003 13-5674085
PAGE 3
022 C000003 115336
022 D000003 974
022 A000004 FIRST BOSTON CORP
022 B000004 13-5659485
022 C000004 99519
022 D000004 2536
022 A000005 SHEARSON LEHMAN AMERICAN EXPRESS
022 B000005 13-2518466
022 C000005 61522
022 D000005 2218
022 A000006 SALOMON SMITH BARNEY HOLD INC
022 B000006 11-2418191
022 C000006 42307
022 D000006 1712
022 A000007 KBC FINANCIAL SERVICES
022 B000007 13-4035459
022 C000007 224
022 D000007 7268
022 A000008 DEUTSCHE BANK CAPITAL CORP
022 B000008 13-2730828
022 C000008 2978
022 D000008 570
022 A000009 HKW & COMPANY
022 B000009 13-1769063
022 C000009 3150
022 D000009 0
022 A000010 CITIGROUP
022 B000010 13-3214963
022 C000010 2799
022 D000010 0
023 C000000 754132
023 D000000 36177
024 000000 Y
025 A000001 LAZARD GROUP LLC
025 B000001 51-0278097
025 C000001 D
025 D000001 788
025 A000002 DELETE
025 D000002 0
025 D000003 0
025 D000004 0
025 D000005 0
025 D000006 0
025 D000007 0
025 D000008 0
026 A000000 N
026 B000000 Y
026 C000000 N
026 D000000 Y
026 E000000 N
026 F000000 N
PAGE 4
026 G010000 N
026 G020000 N
026 H000000 N
027 000000 N
028 A010000 0
028 A020000 0
028 A030000 0
028 A040000 0
028 B010000 0
028 B020000 0
028 B030000 0
028 B040000 0
028 C010000 0
028 C020000 0
028 C030000 0
028 C040000 0
028 D010000 0
028 D020000 0
028 D030000 0
028 D040000 0
028 E010000 0
028 E020000 0
028 E030000 0
028 E040000 0
028 F010000 0
028 F020000 0
028 F030000 0
028 F040000 0
028 G010000 0
028 G020000 0
028 G030000 0
028 G040000 0
028 H000000 0
030 A000000 0
030 B000000 0.00
030 C000000 0.00
031 A000000 0
031 B000000 0
032 000000 0
033 000000 0
035 000000 0
036 B000000 0
038 000000 0
042 A000000 0
042 B000000 0
042 C000000 0
042 D000000 0
042 E000000 0
042 F000000 0
042 G000000 0
042 H000000 0
PAGE 5
043 000000 0
044 000000 0
045 000000 Y
046 000000 N
047 000000 N
048 000000 0.000
048 A010000 0
048 A020000 0.000
048 B010000 0
048 B020000 0.000
048 C010000 0
048 C020000 0.000
048 D010000 0
048 D020000 0.000
048 E010000 0
048 E020000 0.000
048 F010000 0
048 F020000 0.000
048 G010000 0
048 G020000 0.000
048 H010000 0
048 H020000 0.000
048 I010000 0
048 I020000 0.000
048 J010000 0
048 J020000 0.000
048 K010000 0
048 K020000 0.000
049 000000 N
050 000000 N
051 000000 Y
052 000000 N
053 A000000 Y
053 B000000 N
053 C000000 N
054 A000000 Y
054 B000000 Y
054 C000000 Y
054 D000000 N
054 E000000 N
054 F000000 N
054 G000000 Y
054 H000000 Y
054 I000000 N
054 J000000 Y
054 K000000 N
054 L000000 N
054 M000000 Y
054 N000000 N
054 O000000 Y
055 A000000 N
PAGE 6
055 B000000 Y
056 000000 Y
057 000000 N
058 A000000 N
059 000000 Y
060 A000000 Y
060 B000000 Y
061 000000 0
062 A000000 Y
062 B000000 0.0
062 C000000 0.0
062 D000000 0.0
062 E000000 0.0
062 F000000 0.0
062 G000000 0.0
062 H000000 0.0
062 I000000 10.2
062 J000000 0.0
062 K000000 0.0
062 L000000 0.0
062 M000000 0.0
062 N000000 0.0
062 O000000 0.0
062 P000000 81.9
062 Q000000 0.0
062 R000000 18.7
063 A000000 0
063 B000000 6.0
064 A000000 Y
064 B000000 Y
065 000000 N
066 A000000 Y
066 B000000 N
066 C000000 N
066 D000000 N
066 E000000 N
066 F000000 N
066 G000000 Y
067 000000 N
068 A000000 N
068 B000000 N
069 000000 N
070 A010000 Y
070 A020000 N
070 B010000 Y
070 B020000 Y
070 C010000 N
070 C020000 N
070 D010000 N
070 D020000 N
070 E010000 N
PAGE 7
070 E020000 N
070 F010000 N
070 F020000 N
070 G010000 N
070 G020000 N
070 H010000 N
070 H020000 N
070 I010000 N
070 I020000 N
070 J010000 Y
070 J020000 Y
070 K010000 N
070 K020000 N
070 L010000 Y
070 L020000 Y
070 M010000 N
070 M020000 N
070 N010000 N
070 N020000 N
070 O010000 Y
070 O020000 Y
070 P010000 N
070 P020000 N
070 Q010000 N
070 Q020000 N
070 R010000 N
070 R020000 N
071 A000000 84612
071 B000000 117862
071 C000000 240269
071 D000000 35
072 A000000 12
072 B000000 22397
072 C000000 1743
072 D000000 0
072 E000000 0
072 F000000 3198
072 G000000 0
072 H000000 0
072 I000000 48
072 J000000 -84
072 K000000 0
072 L000000 120
072 M000000 180
072 N000000 0
072 O000000 79
072 P000000 1686
072 Q000000 0
072 R000000 128
072 S000000 300
072 T000000 0
PAGE 8
072 U000000 0
072 V000000 0
072 W000000 114
072 X000000 5769
072 Y000000 0
072 Z000000 18371
072AA000000 22760
072BB000000 7228
072CC010000 2200
072CC020000 0
072DD010000 19033
072DD020000 0
072EE000000 1675
073 A010000 2.1100
073 A020000 0.0000
073 B000000 0.1800
073 C000000 0.0000
074 A000000 5461
074 B000000 0
074 C000000 24115
074 D000000 193400
074 E000000 5657
074 F000000 31103
074 G000000 0
074 H000000 0
074 I000000 7472
074 J000000 917
074 K000000 0
074 L000000 5023
074 M000000 49
074 N000000 273197
074 O000000 0
074 P000000 738
074 Q000000 20000
074 R010000 0
074 R020000 0
074 R030000 0
074 R040000 16184
074 S000000 0
074 T000000 236275
074 U010000 9064953
074 U020000 0
074 V010000 26.06
074 V020000 0.00
074 W000000 0.0000
074 X000000 11836
074 Y000000 0
075 A000000 0
075 B000000 230123
076 000000 30.05
077 A000000 Y
PAGE 9
077 B000000 Y
077 C000000 Y
077 E000000 Y
077 Q010000 Y
077 Q020000 Y
077 Q030000 N
078 000000 N
080 A000000 NATIONAL UNION FIRE INS. CO. OF PITTSBURGH PA
080 B000000 NONE
080 C000000 1275
081 A000000 Y
081 B000000 1
082 A000000 N
082 B000000 0
083 A000000 N
083 B000000 0
084 A000000 N
084 B000000 0
085 A000000 Y
085 B000000 N
086 A010000 87
086 A020000 2376
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
087 A010000 COMMON SHARES
087 A020000 576292106
087 A030000 MCI
088 A000000 Y
088 B000000 N
088 C000000 N
088 D000000 N
SIGNATURE CHARLES C. MCCOBB, JR.
TITLE V.P. AND C.F.O.
EXHIBIT INDEX TO FORM N-SAR
OF MASSMUTUAL PARTICIPATION INVESTORS
FOR ANNUAL PERIOD ENDED DECEMBER 31, 2005
EXHIBIT NO. DESCRIPTION
77B Accountant's Report on Internal Controls
77E Legal Proceedings
77Q2 Information Called For by Item 405 of Regulation S-K