Present address: Hagoromo Foods Corporation. 151, Shimazaki-cho, Shimizu-shi, Shizuoka 424-85. Japan.The seasonal variation offatty acid composition in lipids of various organs and stomach contents of bonito (Euthynnus pelamis) was investigated. Although docosahexaenoic acid in the lipids of the stomach contents originating from their prey organisms varied from about 13% to 31%, it was the dominant unsaturated fatty acid andaccounted for more than 25% of the total fatty acids in the lipids of every organ of bonito in and out of season, and its seasonal variation was comparatively small.