To validate the usefulness of recombinant CYP enzymes in metabolic studies of optically active drugs, enantiomer selectivity was examined for oxidation of optically active R-blokers by rat CYP2D enzymes (CYP2D1, -2D2, -2D3 and -2D4) and human CYP2D6 expressed in yeast cells, and was compared with the profile of liver microsomes (Ms). In bunitrolol (BTL) 4hydroxylation rate, selectivity of [(+)-BTL<(-)-BTL] was obtained for rat liver Ms, whereas a reversed selectivity was observed for CYP2D2 that was only one BTL 4-hydroxylase among the rat CYP2D enzymes examined. In propranolol (PL) 4-, 5 and 7-oxidation and N-desisopropylation, rat liver Ms exhibited selectivity of [R(+)-PL>S(-)-PL] in a low PL concentration range. CYP2D2 having the highest PL oxidation activities among the rat CYP2D enzymes showed selectivity of [R(+)PL<S(-)-PL] only for PL 4-hydroxylation while selectivity for other indices was the same between rat liver Ms and the recombinant CYP2D2. Human liver Ms yielded selectivity of [R(+)-PL>S(-)-PL] in a low PL concentration range, whereas recombinant CYP2D6 did not show clear selectivity. PL oxidation by human CYP2D6 showed biphasic kinetics. Kinetics of racemic bufuralol (BUF) were monophasic for rat CYP2D2 and human CYP2D6 but biphasic for rat CYP2D4. Considering these results, different enantioselectivity between liver Ms and recombinant CYP2D enzymes and biphasic kinetics for recombinant CYP enzymes may be caused by different microenvironments surrounding CYP enzymes between liver and yeast cells.