Seven oxygenated sterols were tested for their effect on cholesterol biosynthesis from 24, 25-dihydrolanosterol by rat hepatic subcellular 10000 x g supernatant fraction. The sterols (40 μM) exhibited considerable inhibitory effects on the synthesis of cholesterol from [24, 25-³H]-24, 25-dihydrolanosterol (18 μM). 5α-Cholest-8 (14)-en-3β-ol-15-one had the greatest effect (64% inhibition). The biological importance of the inhibitory properties of the sterols is discussed.