The method, which is suitable for algae down to 2 μ in diameter, determines the weight of total fatty acids (however originally combined) and total unsaponifiable fat-soluble matter in fresh algal material containing 20–280 mg total dry matter. The chemical treatment is based on that of Belin (1926). Experience with variations of the method on several algal species is described. Preliminary Soxhlet extraction with 95% ethanol for 18 h removed virtually all the lipid from the algae, ready for purification and further analysis, in the cases of Chlorella marina, C. vulgaris and Scotiella sp. (Chlorophyceae), Tribonema aequale (Xanthophyceae), Isochrysis galbana (Chrysophyceae) and Phaeodactylum tricornutum (Bacillariophyceae). This extraction was not efficient, however, in the cases of two members of the Myxophyceae (Anabaena cylindrica and Microcoleus vaginatus) and one of the Rhodophyceae (Porphyridium cruentum). The fat metabolism of these two classes is known to differ from that of other classes, but a similar inefficiency in the case of Monodus subterraneus (Xanthophyceae) is unexplained. In such cases supplementary processes were necessary to achieve full extraction. The methods are described in detail.