CORYNOMYCOLIC acid, C32H64O3, m.p. 70°, [α]D = + 7.5° has been isolated from the lipids of Corynebacterium diphtheriae 1 and C. ovis 2. Its structure (III, R = H) has been established by degradation3 and confirmed by synthesis: the condensation of two molecules of methyl palmitate (I, R = CH3) in presence of NaH gives the β-ketoester (II, R = CH3) which is reduced by NaBH4 to a mixture of two diastereo-isomers (III, R = CH3)4; one of these has been shown to be racemic methyl corynomycolate5.