The sterol content of two Myxomycetes, Physarum polycephalumand P. flavicomumhas been examined. The sterols of the two species are apparently identical, the two major sterols in each being poriferasterol and 22-dihydroporiferasterol. Threee minor sterols are probably Δ5-ergostenol, ergostanol, and poriferastanol. The triterpenoids of the two species differ in that, though lanosterol was identified in both, 22-dihydrolanosterol was indicated only in P. flavicomum. The occurrence of lanosterol together with a typical mixture of plant sterols is somewhat unusual.