Some new methods for separation and investigation of sterols, developed by us, and their applications are discussed. The sterol composition of seven sponges from the Black Sea (Dysidea ƒragilis, Haliclona flavescens, Haliclona aquaeductus, Haliclona cinerea, Halichondria panicea, Lissodendoryx variisclera and Crella gracilis) was compared. 4-Methyl sterols were found only in two of the investigated Haliclona species. More than fifty-five sterols, six of them new ones, were found in the investigated sponges. Biosynthesis of sterols in them and their application in the taxonomy of sponges are discussed. Our earlier investigations on sterols from Black Sea Coelenterata (5 species), mussels (7 species), snails (3 species), Bryozoans (1 species) and Tunicates (2 species) are briefly discussed. Sterol composition and biosynthesis are compared.