_ _ _ _ _ _ _~ _ _ _~ ____Growth of the yeast Saccharomycopsis lipolytica on n-alkanes induced a hydroxylation system which, in the presence of NADPH and O,, converted lauric acid into u-hydroxylauric acid. The specific hydroxylation activity was lower with the physiological substrate n-hexadecane than with lauric acid. This system was particulate and did not act on Nand O-dealkylated compounds. It was strongly inhibited by CO and its enzymic activity was unstable. Because of the presence of cytochrome oxidase in the preparations, spectral demonstration of the presence of cytochrome P-450 was difficult but could be achieved with the techniques developed.