The mechanisms by which 2(3)-tert-butyl-4-hydroxyanisole (BHA) protects against chemical carcinogenesis and toxicity include enhancement of the activities of several detoxification enzymes. In previous studies, 14-day administration of BHA to female CD-1 mice at 0.75% of the diet led to large increases in cytosolic glutathione transferase (EC 2.5.1.18) and reduced nicotinamide adenine dinucleotide (phosphate) dehydrogenase (quinone) (EC 1.6.99.2) [NAD(P)H:quinone reductase; DT-diaphorase] specific activities in several tissues, and elevated hepatic glutathione transferase messenger RNA. In the present study, one day of dietary BHA significantly increased NAD(P)H:quinone reductase and glutathione transferase activities in the liver, kidney, and proximal small intestine, and NAD(P)H:quinone reductase activity in the forestomach and lung. In the proximal small intestine, glutathione transferase specific activities toward 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene rose to 2.6 and 8 times those of control, respectively, and NAD(P)H:quinone reductase specific activity doubled, within 1 day on the BHA diet. Six hr after a single p.o. dose of BHA (620 mg/kg), intestinal glutathione transferase specific activities were 30 to 50% above those of control mice. In liver, the kinetics of increase of glutathione transferase messenger RNA were in accord with increased synthesis as the mechanism of elevation of glutathione transferase activity in response to BHA. Although changes in mixed-function oxygenase activities have been reported to occur more rapidly, the kinetics of the response of glutathione transferase and NAD(P)H:quinone reductase specific activities to BHA indicates that nonoxidative detoxification potential is substantially enhanced within 24 hr or less after initiation of BHA administration.