Content of 14C-phenazepame and its metabolites was studied in feces and urine of mice strains C57BL/6 and BALB/ c after intraperitoneal administration of the preparation at a dose of 14 mg/kg. Concentration of phenazepame and of its trihydroderivative was higher in urine of the BALB/c strain mice than in C57BL/6 strain that corresponded to genetic differences of the tranquilizer metabolism in the animal strains studied.