Incubation of the microsomal fraction from etiolated wheat shoots (Triticum aestivum L. cv Etoile de Choisy) with [1-14C]oleic acid led to the formation of three polar metabolites which were identified as 18-, 17- and 16-hydroxyoleic acids by gas chromatography/mass spectra analysis. They were generated in a molar ratio of 1.4/4.6/4, respectively. Terminal and sub-terminal hydroxylation of oleic acid and the cytochrome P450 content were strongly enhanced in microsomes from wheat shoots treated with naphthalic acid anhydride and phenobarbital. The involvement of cytochrome P450 is demonstrated by the dependence of hydroxylation upon O2 and NADPH, and by their light-reversible inhibition by carbon monoxide. In addition, the hydroxylation of oleic acid, but not of lauric acid and cinnamic acid, was inhibited when microsomes where incubated with 9-octadecen-16-ynoic acid, a substrate analogue displaying an acetylenic function at the carbon position of major enzyme attack. Our results suggest that at least two different P450 enzymes are involved in the oxidation of oleic and lauric acids in wheat.