The effects of oral luteolin on the N-acetylation and metabolism of 2-aminofluorene (AF) in vivo were investigated in bladder, blood, colon, kidney, liver, feces, urine, cerebrum, cerebellum and pineal gland from male Sprague-Dawley rats. Major metabolites such as AAF, 1-OH-AAF, 3-OH-AAF, 8-OH-AAF and 9-OH-AAF were found in bladder tissues; AAF, 1-OH-AAF, 5-OH-AAF and 8-OH-AAF were found in blood samples; AAF, 1-OH-AAF, 3-OH-AAF, 5-OH-AAF, 8-OH-AAF and 9-OH-AAF were found in colon tissues; AAF, 1-OH-AAF, 3-OH-AAF and 9-OH-AAF were found in kidney tissues; AAF, 1-OH-AAF, 3-OH-AAF and 8-OH-AAF were found in liver tissues, AAF, 1-OH-AAF, 3-OH-AAF, 5-OH-AAF, 7-OH-AAF, 8-OH-AA and 9-OH-AAF were found in feces and urine samples; AAF, 1-OH-AAF, 3-OH-AAF and 8-OH-AAF were found in cerebrum tissues; AAF, 1-OH-AAF, 3-OH-AAF and 7-OH-AAF were found in cerebellum tissues; but only AF and AAF were found in pineal gland in rats treated with AF (50 mg/kg) for 24 h. Pretreatment of rats with luteolin (30 mg/kg) 24 h prior to the administration of AF (50 mg/kg) and luteolin given with AF concomitantly led to a decrease in the amounts of 3-OH-AAF and 9-OH-AAF and an increase in the amounts of 1-OH-AAF and 8-OH-AAF in bladder tissues. In blood samples, there were significant decreases of AAF, 1-OH-AAF and 8-OH-AAF after rats were treated with luteolin for 24 h prior to AF but luteolin with AF at the same time caused an increase in 1-OH-AAF. In colon tissues, there were significant decreases of AF, 1-OH-AAF, 3-OH-AAF, 5-OH-AAF and 9-OH-AAF after rats were treated with luteolin for 24 h then AF but the amounts of AF, 1-OH-AAF, 5-OH-AAF and 9-OH-AAF decreased and AAF and 8-OH-AAF increased in rats treated with luteolin and AF at the same time. In kidney tissues, there were significant decreases of AF, AAF and 3-OH-AAF after rats were treated with both compounds at the same time, but luteolin for 24 h then AF treatment led to significant decreases of 3-OH-AAF. In liver samples, after rats were treated with luteolin and AF at the same time, the amounts of AAF and 1-OH-AAF significantly decreased but 8-OH-AAF increased. However, rats treated with luteolin for 24 h then with AF led to significant decreases of AAF, 1-OH-AAF and 3-OH-AAF. In feces samples, there were significant increases of AAF, 3-OH-AAF, 7-OH-AAF, 8-OH-AAF and 9-OH-AAF after rats were treated with both compounds at the same time but luteolin for 24 h then AF treatment led to a significant increase of AF, 1-OH-AAF and 8-OH-AAF and a decrease AAF and 3-OH-AAF. In urine samples, there were significant increases of AF, AAF, 1-OH-AAF, 3-OH-AAF, 5-OH-AAF and 9-OH-AAF but a decrease of 8-OH-AAF after rats were treated with both compounds at the same time. However, the luteolin for 24 h then AF treatment led to significant increases of AF, AAF and 1-OH-AAF but decreases of 3-OH-AAF and 5-OH-AAF. In cerebrum samples, there were significant increases ofAF but decreases of 1-OH-AAF and 8-OH-AAF after rats were treated with both compounds at the same time; luteolin for 24 h then AF treatment of rats led to significant increase of 1-OH-AAF and decreases AF, AAF and 8-OH-AAF. In cerebellum samples, there were significant increases of AAF and decreases of 1-OH-AAF and 3-OH-AAF after rats were treated with both compounds at the same time, there is a significant increase of AAF but decrease of 1-OH-AAF, 3-OH-AAF and 7-OH-AAF after the luteolin treated for 24 h then AF were treated to the rats. In pineal gland samples, there were significant increases ofAAF after rats were treated with both compounds at the same time. However, luteolin treated for 24 h then AF were treated to the rats which increase AAF but decrease AF.