In 1941, Fernholz and Ruigh (1) convincingly demonstrated that campesterol and campestanol differ from 22,23-dihydrobrassicasterol and ergostanol solely in the optical configuration at C-24. Since then it has been shown that this C-24 epimerism is not infrequently encountered among naturally occurring sterols, and that the C2s-sterols from marine invertebrates such as the stellasterols and stellastenols (2), neospongosterol (3) and chalinasterol (4) predominantly belong to the campestanol series. In conformity with the customary designation of steroid epimers, it is here proposed to refer to the ergostanol and campestanol series as the 24-(a)-and 24-(0)-methylcholestanol series, and following a suggestion by Ruigh (5), to write the 24-methyl group above the side chain in the «-series (I) and below the side chain in the 0-series (II).