Antibodies to cytochromes P-450NMa and P-450NMb (CYP2A and CYP2G1, respectively) (P-450 nomenclature by Nebert et al., DNA Cell Biol. 10, 1- (1-14) 14, 1991) were used to assess the effects of the herbicide dichlobenil on the distribution of these olfactory-specific isozymes in the olfactory mucosa. Twenty-eight hours after a single dose (12 mg/kg) of dichlobenil, characteristic regions of the olfactory mucosa showed signs of necrosis in H&E stained sections. Accompanying this was a dramatic reduction in P-450 immunoreactivity in Bowman's glands of the olfactory mucosa, and an apparent redistribution of P-450 immunoreactivity within sustentacular cells. Treatment of mice with metyrapone, a P-450 inhibitor, at 10 min prior to and 2, 4, 6, and 8 h after a single dichlobenil injection, provided some protection against the damaging effects of dichlobenil. Both the gross and subcellular appearance of P-450 immunoreactivity in metyrapone/dichlobenil treated mice was similar to controls. Western blot analysis of P-450 expression following dichlobenil or metyrapone/dichlobenil treatment was generally consistent with immunohistochemical findings. These studies support previous reports that dichlobenil-induced olfactotoxicity is cytochrome P-450 mediated.