Cryptosterol (C30H50O) isolated from yeast and isomerie lanosterol from sheep wool are very similar. They and their corresponding derivatives have about the same melting points, color reactions and optical rotation. To determine the position of the active double bonds, 1 gm. of cryptosterol is dissolved in hot acetic acid and a 3% stream of ozone passed through the soln. When sufficient ozone has been used to correspond to one double bond and the soln. has become clear, the soln. is poured into 5 vols. of water and the ozonide obtained as a precipitate. The soln. is carefully distilled, 2.4-dinitrophenylhydrazine added to the distillate and acetone 2,4-dinitrophenylhydrazine, m.p. 128[degree], obtained. Acetone is obtained from lanosterol in a similar manner. Dihydro-cryptosterol does not react with ozone. Cryptosterol and lanosterol have the active hydrogenateable double bond in an isopropylidene group, [image] .By addition of osmium tetraoxide to cryptosterol, cryptostenetriol is prepd., from which 80% of the theoretical yield of acetone is obtained by dehydrogenation with Pb acetate. The double bond of cryptosterol, which is slow to react, is oxidized with perbenzoic acid to yield an oxido compound. Cryptosterol and lanosterol differ from each other only in the position of this double bond, which reacts slowly, and otherwise they have the same structure and configuration.