AbstractThe present study reports the modulatory influence of alcoholic extract from the leaves of Ocimum sanctum on the activities of cytochrome p‐450, cytochrome b5, and aryl hydrocarbon hydroxylase enzymes in the liver and glutathione‐S‐transferase and reduced glutathione level in the liver, lung, and stomach of the mouse. Oral treatment with the leaf extract at 400 and 800 mg/kg body wt for 15 days would significantly elevate the activities of cytochrome p‐450 (p<0.05), cytochrome b5(p<0.01, p<0.001), aryl hydrocarbon hydroxylase (p<0.05), and glutathione S‐transferase (p<0.05, p<0.01), all of which are important in the detoxification of carcinogens as well as mutagens. Moreover treatment with 400 and 800 mg/kg body wt of Ocimum extract for 15 days also significantly elevated extrahepatic glutathione‐S‐transferase (p<0.05, p<0.01). The reduced glutathione level was also elevated by treatment with the leaf extract in liver, lung, and stomach tissues (p<0.01, p<0.001). Mice fed a diet containing 0.75% butylated hydroxyanisole (positive control) revealed no alteration in the basal hepatic cytochrome p‐450 and aryl hydrocarbon hydroxylase level, but hepatic cytochrome b5and glutathione S‐transferase activity in hepatic and extrahepatic organs were elevated in a time‐responsive manner (p<0.05, p<0.001). The observations suggest further exploitation of the Ocimum leaf extract or its active principle(s) for the chemoprevention of chemical carcinogenesis in different animal model systems.