It has been reported that N-(α-methylbenzyl) linoleamide (MBLA) had a remarkable cholesterol-lowering effect on the experimental hypercholesterolemia in rabbits and rats.There are three optical isomers of MBLA: D-, L- and DL-MBLA because of an asymmetric carbon atom in the amine moiety of MBLA. And the potency of the cholesterol-lowering effect was found to be the following order: D->DL->L-MBLA.Fukushima also found that the respiratory excretion of 14C after oral administration of carboxy 14C-labeled L-MBLA to rats was significantly greater than that of D- or DL-MBLA, whereas the ratio of urinary 14C excretion of D-MBLA was higher than that of L- or DL-MBLA. These results suggest that the difference of the cholesterol-lowering potency observed among the MBLA isomers might be closely related with the difference of biological disposition of the isomers.The present paper describes the results of in vitro studies on the enzymatic hydrolysis of the amide linkage of MBLA isomers.