Monooxygenase enzymatic activities were measured in liver and kidney microsomes of control and ethanol-treated rats. Animals were administered alcohol by using a model for alcoholic liver injury. Several in vitro approaches were used to compare the laurate metabolism in liver and kidney microsomes: correlation studies between specific P-450 catalytic activities, immunoblot analysis, and chemical and immunoinhibitions. Ethanol treatment increased the liver and renal hydroxylations of chlorzoxazone and 4-nitrophenol. Moreover, lauric acid (omega-1)-hydroxylation was found to be significantly increased (∼6-fold) after ethanol treatment in liver, but not in kidney microsomes. The laurate omega-1/omega ratio increased from 1.52 ± 0.49 to 4.11 ± 1.01 in liver microsomes of control and ethanol-treated rats, and from 0.29 ± 0.06 to 0.44 ± 0.07 in kidney microsomes. Immunoblot analysis using polyclonal anti-cytochrome P-450 (CYP) 2E1 or CYP4A antibodies showed an increase of CYP2E1 and CYP4A contents in both organs, but the increase was higher in liver than in kidney microsomes. Chemical inhibitions using CYP2E1 competitive inhibitors (such as chlorzoxazone and ethanol) led to a nonsignificant inhibition of the renal (omega-1)-hydroxylation of lauric acid. In contrast, 17-octadecynoic acid (a mechanism-based inhibitor of omega-hydroxylase) was able to inhibit both omega- and (omega-1)-hydroxylations of lauric acid in kidney microsomes. Immunoinhibitions specific to CYP2E1 significantly decreased the (omega-1)-hydroxylation of lauric acid in liver, but not in kidney microsomes, whereas the polyclonal anti-CYP4A1 antibody inhibited omega- and (omega-1)-hydroxylations of lauric acid in kidney microsomes. All of these results show that lauric acid hydroxylations in liver and kidney respond in different manners to ethanol treatment. Lauric acid (omega-1)-hydroxylation, a highly specific probe for CYP2E1 in rat and human liver microsomes, is mediated by a CYP4A isoform in rat kidney microsomes.