Rabbit antibodies raised against the major isozymes of cytochrome P-450 isolated from hepatic microsomes of beta-naphthoflavone- (BNF) and phenobarbital-treated rats (cytochrome P-450 BNF-B2 and cytochrome P-450 PB-B2, respectively) and against rat liver NADPH-cytochrome P-450 reductase were used to localize these enzymes immunohistochemically in the rat ventral prostate. Using the unlabeled antibody peroxidase-antiperoxidase technique, NADPH-cytochrome P-450 reductase was detected exclusively in the epithelial cells of the gland to the same magnitude in untreated, phenobarbital-, and BNF-treated rats. Cytochrome P-450 BNF-B2-like immunoreactivity was exclusively present in the glandular epithelium in BNF-treated rats, whereas staining could not be visualized in untreated or in phenobarbital-treated rats. The staining for NADPH-cytochrome P-450 reductase was more uniformly distributed within the epithelium than was the cytochrome P-450 BNF-B2-like immunoreactivity. Cytochrome P-450 PB-B2-like immunoreactivity was not found, regardless of animal pretreatment. These findings support our previous results (Haaparanta, T., Halpert, J., Glaumann, H., and Gustafsson, J-A., Cancer Res. 43: 5131-5137, 1983) demonstrating the presence of constitutive NADPH-cytochrome P-450 reductase in the prostate and that an isozyme of cytochrome P-450 is highly inducible by BNF in this gland. The significance of these findings are discussed in view of the essentially unknown etiology of human prostatic cancer.