Purified flagella of the eukaryotic algaChlamydomonas reinhardi have a sterol composition (55% ergosterol [24β-methylcholesta-5,7,22-trans-trien-3β-ol] and 45% 7-dehydroporiferasterol [24β-ethylcholesta-5,7,22-trans-trien-3β-ol]) identical of that of the whole algal cell. Fatty acids isolated fromC. reinhardi flagella were identified as 16∶0, 18∶0, 18∶1, 18∶2 and 18∶3. Whole cell fatty acids included 14∶0, 16∶2 and 16∶3 in addition to those found in the flagella. Triunsaturates comprised 22.9% of the flagellar fatty acids and 76.4% of those from the whole cell.