PAGE 1 000 A000000 03/31/2015 000 C000000 0000884121 000 D000000 N 000 E000000 NF 000 F000000 Y 000 G000000 N 000 H000000 N 000 I000000 6.1 000 J000000 A 001 A000000 TEKLA LIFE SCIENCES INVESTORS 001 B000000 811-6565 001 C000000 6177728500 002 A000000 100 Federal Street, 19th Floor 002 B000000 BOSTON 002 C000000 MA 002 D010000 02110 003 000000 N 004 000000 N 005 000000 N 006 000000 N 007 A000000 N 007 B000000 0 007 C010100 1 008 A000001 TEKLA CAPITAL MANAGEMENT LLC 008 B000001 A 008 C000001 801-000000 008 D010001 BOSTON 008 D020001 MA 008 D030001 02110 010 A000001 STATE STREET BANK AND TRUST CO. 010 B000001 85-85003 010 C010001 BOSTON 010 C020001 MA 010 C030001 02111 012 A000001 COMPUTERSHARE TRUST CO. N.A. 012 B000001 85-113400 012 C010001 CANTON 012 C020001 MA 012 C030001 02021 013 A000001 DELOITTE & TOUCHE LLP 013 B010001 BOSTON 013 B020001 MA 013 B030001 02110 015 A000001 STATE STREET BANK & TRUST CO. 015 B000001 C 015 C010001 BOSTON 015 C020001 MA 015 C030001 02110 015 E010001 X 018 000000 Y 019 A000000 Y PAGE 2 019 B000000 3 019 C000000 TEKLAFUNDS 020 A000001 J P MORGAN SECURITIES INC 020 B000001 13-3224013 020 C000001 32 020 A000002 BANK OF NEW YORK MELLON 020 B000002 13-5160382 020 C000002 27 020 A000003 NATIONAL FINANCIAL SERVICES CORP. 020 B000003 04-2785576 020 C000003 19 020 A000004 BANK OF AMERICA CORP. 020 B000004 95-4035346 020 C000004 17 020 A000005 OPPENHEIMER & CO., INC. 020 B000005 13-2527171 020 C000005 11 020 A000006 MIZUHO CORPORATE BANK LTD. 020 B000006 13-5624234 020 C000006 9 020 A000007 Wells Fargo Securities, LLC 020 B000007 94-3379992 020 C000007 8 020 A000008 JEFFERIES & CO. 020 B000008 95-2622900 020 C000008 8 020 A000009 BARCLAYS BANK 020 B000009 06-1031656 020 C000009 8 020 A000010 PIPER JAFFRAY & CO. 020 B000010 41-0953246 020 C000010 7 021 000000 156 022 A000001 STATE STREET BANK AND TRUST CO. 022 B000001 04-1867445 022 C000001 239900 022 D000001 0 022 A000002 BANK OF NEW YORK MELLON 022 B000002 13-5160382 022 C000002 4435 022 D000002 0 022 A000003 JEFFERIES & CO. 022 B000003 95-2622900 022 C000003 2295 022 D000003 0 022 A000004 NATIONAL FINANCIAL SERVICES CORP. 022 B000004 04-2785576 022 C000004 1800 022 D000004 0 022 A000005 BANK OF AMERICA CORP. 022 B000005 95-4035346 PAGE 3 022 C000005 1660 022 D000005 0 022 A000006 CARDIOKINETIX, INC. 022 C000006 1378 022 D000006 251 022 A000007 Veniti, Inc. 022 C000007 820 022 D000007 0 022 A000008 Insightra Medical, Inc. 022 C000008 775 022 D000008 0 022 A000009 NEUROVANCE, INC 022 C000009 544 022 D000009 0 022 A000010 MIZUHO CORPORATE BANK LTD. 022 B000010 13-5624234 022 C000010 0 022 D000010 367 023 C000000 253995 023 D000000 618 024 000000 N 026 A000000 N 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 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 PAGE 4 028 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 0 043 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 PAGE 5 048 J010000 0 048 J020000 0.000 048 K010000 0 048 K020000 0.000 049 000000 N 050 000000 N 051 000000 N 052 000000 N 053 A000000 Y 053 B000000 Y 053 C000000 N 054 A000000 Y 054 B000000 N 054 C000000 Y 054 D000000 N 054 E000000 N 054 F000000 N 054 G000000 N 054 H000000 N 054 I000000 N 054 J000000 Y 054 K000000 N 054 L000000 N 054 M000000 Y 054 N000000 N 054 O000000 N 055 A000000 N 055 B000000 N 056 000000 N 057 000000 N 058 A000000 N 059 000000 Y 060 A000000 Y 060 B000000 Y 061 000000 0 062 A000000 N 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 0.0 062 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 0.0 PAGE 6 062 Q000000 0.0 062 R000000 0.0 063 A000000 0 063 B000000 0.0 066 A000000 Y 066 B000000 N 066 C000000 Y 066 D000000 N 066 E000000 N 066 F000000 N 066 G000000 N 067 000000 N 068 A000000 N 068 B000000 N 069 000000 N 070 A010000 Y 070 A020000 Y 070 B010000 Y 070 B020000 N 070 C010000 N 070 C020000 N 070 D010000 Y 070 D020000 N 070 E010000 N 070 E020000 N 070 F010000 Y 070 F020000 N 070 G010000 Y 070 G020000 N 070 H010000 Y 070 H020000 N 070 I010000 N 070 I020000 N 070 J010000 Y 070 J020000 Y 070 K010000 Y 070 K020000 Y 070 L010000 Y 070 L020000 Y 070 M010000 Y 070 M020000 Y 070 N010000 Y 070 N020000 N 070 O010000 Y 070 O020000 N 070 P010000 N 070 P020000 N 070 Q010000 N 070 Q020000 N 070 R010000 Y 070 R020000 N PAGE 7 071 A000000 83941 071 B000000 119211 071 C000000 467187 071 D000000 18 072 A000000 6 072 B000000 218 072 C000000 270 072 D000000 0 072 E000000 0 072 F000000 2506 072 G000000 35 072 H000000 0 072 I000000 28 072 J000000 45 072 K000000 26 072 L000000 18 072 M000000 91 072 N000000 0 072 O000000 0 072 P000000 0 072 Q000000 0 072 R000000 56 072 S000000 126 072 T000000 0 072 U000000 0 072 V000000 0 072 W000000 73 072 X000000 3004 072 Y000000 133 072 Z000000 -2383 072AA000000 42548 072BB000000 0 072CC010000 50890 072CC020000 0 072DD010000 0 072DD020000 0 072EE000000 18514 073 A010000 0.0000 073 A020000 0.0000 073 B000000 0.9700 073 C000000 0.0000 074 A000000 35747 074 B000000 0 074 C000000 0 074 D000000 11093 074 E000000 28888 074 F000000 453786 074 G000000 0 074 H000000 0 074 I000000 0 074 J000000 2812 PAGE 8 074 K000000 0 074 L000000 142 074 M000000 159 074 N000000 532627 074 O000000 6858 074 P000000 415 074 Q000000 0 074 R010000 0 074 R020000 0 074 R030000 0 074 R040000 279 074 S000000 0 074 T000000 525075 074 U010000 19321 074 U020000 0 074 V010000 27.18 074 V020000 0.00 074 W000000 0.0000 074 X000000 208 074 Y000000 0 075 A000000 0 075 B000000 487823 076 000000 27.57 077 A000000 N 078 000000 N 080 C000000 0 081 B000000 0 082 B000000 0 083 B000000 0 084 B000000 0 086 A010000 315 086 A020000 8447 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 TEKLA LIFE SCIENCES INVESTORS 087 A020000 87911K100 087 A030000 HQL 088 A000000 N 088 B000000 N 088 C000000 N 088 D000000 N SIGNATURE LAURA WOODWARD TITLE TREASURER