1. 1. Sterol compositions of 14 species of Crustacea were determined by high-resolution gas-liquid chromatography (GLC). 2. 2. Cholesterol was the major sterol in all species and comprised from 99 to 100 per cent of the total sterol in the euphausid, Nyctiphanes norvegica, 4 species of the suborder Macrura, and i species of the Brachyura. Geryon quinquedens. 3. 3. Desmosterol, when it was present, was the second principal sterol. 4. 4. Six other minor sterols were identified in certain species by comparing the retention times on GLC with 37 reference sterols. 5. 5. Thin-layer chromatography and mass spectrometry were used to search for cholestanol in 5 species of Crustacea but none was detected. 6. 6. There was no variation in the sterol compositions of May, July, and October samples of Chionoecetes opilio, suggesting that there is little or no seasonal variation. 7. 7. Species of the suborder Macrura had higher average total lipid, unsaponifiable, and sterol contents than species of the suborder Brachyura. The range of total sterol in the former group was 70–140 mg. per 100 g. wet weight of tissue and m the latter 40–100 mg. per 100 g.