Fatty acid composition and total lipid content of 8 strains of marine diatoms (Nitzschia frustrula, Nitzschia closterium, Nitzschia incerta, Navicula pelliculosa,Phaeodactylum tricornutum, Synedra fragilaroides) were examined. The microalgae were grown under defined conditions and harvested at the late exponential phase. The major fatty acids in most strains were 14:0 (1.0%-6.3%), 16:0 (13.5%-26.4%), 16:1n-7 (21.1%-46.3%) and 20:5n-3 (6.5%-19.5%). The polyunsaturated fatty acids 16:2n-4, 16:3n-4, 16:4n-1 and 20:4n-6 also comprised a significant proportion of the total fatty acids in some strains. The characteristic fatty acid composition of diatoms is readily distinguishable from those of other microalgal groups. Significant concentration of the polyunsaturated fatty acid 20:5n-3 (eicosapentaenoic acid) was present in each strain, with the highest proportion in B222 (19.5%).