Cytochrome P-450 from Bacillus megaterium catalyses the diastereoselective hydroxylations of 13-hydroxymyristic acid, to predominantly erythro-12,13-dihydroxymyristic acid, and of 12-hydroxymyristic acid to give predominantly threo-12,13-dihydroxymyristic acid, in reactions that are stereocomplementary and with considerable potential application in biotransformations.