The effects of ellagic acid on the in vivo N-acetylation and metabolism of 2-aminofluorene (2-AF) were investigated in bladder, blood, colon, kidney, liver, feces and urine samples from male Sprague-Dawley rats. Major metabolites such as 1-OH-2-AAF, 8-OH-2-AAF and 9-OH-2-AAF were found in bladder tissues, 1-OH-2-AAF, 5-OH-2-AAF and 8-OH-2-AAF were found in blood samples, 1-OH-2-AAF, 3-OH-2-AAF, 5-OH-2-AAF, 8-OH-2-AAF and 9-OH-2-AAF were found in colon tissues, 1-OH-2-AAF, 3-OH-2-AAF and 9-OH-2-AAF were found in kidney tissues, 1-OH-2-AAF, 3-OH-2-AAF and 8-OH-2-AAF were found in liver tissues, 1-OH-2-AAF, 3-OH-2-AAF, 5-OH-2-AAF and 8-OH-2-AAF were found in feces samples and 1-OH-2-AAF, 3-OH-2-AAF, 5-OH-2-AAF and 8-OH-2-AAF were also found in urine samples after rats had been orally treated with 2-AF (50 mg/kg) for 24 h. Pretreatment of male rats with ellagic acid (10 mg/kg) 24 h prior to the administration of 2-AF (50 mg/kg) resulted in absence of 8-OH-2-AAF in bladder tissues, and there were significant decreases of 8-OH-2-AAF in blood and urine samples. In blood samples, amounts of 2-AAF and 8-OH-2-AAF were significantly decreased; in colon tissues, amounts of 2-AF, 1-OH-2-AAF and 3-OH-2-AAF, in liver tissues, amounts of 2-AAF, 1-OH-2-AAF and 3-OH-2-AAF, and in urine samples, amounts of 2-AF and 8-OH-2-AAF were significantly decreased in 24-h ellagic acid (EA)-treated rats before 2-AF was added to the diet. However, significantly increased 1-OH-2-AAF concentrations were found in urine samples in 24-h EA-treated rats before 2-AF was administered. In the EA and 2-AF rats, in the same time treated groups, bladder, colon and liver tissues, and feces and urine samples showed significant differences when compared to the ones without EA co-treatment. We saw significant decreases of the amounts of 2-AF and 1-OH-2-AAF in colon tissues. The feces samples showed increased amounts of 2-AAF in EA- and in 2-AF- treated rats in the same time groups, but urine samples showed a decreased amount of 8-OH-2-AAF in both EA-treated groups. The total amounts of 2-AF metabolites in bladder, blood, kidney and liver tissues showed significant difference between control and the group which was EA-treated 24 h before 2-AF was added. The total amounts of 2-AF metabolites in the liver, feces and urine showed significant decreases between control and EA-treated at the same time with 2-AF groups. This is the first report of EA affecting the N-acetylation and metabolism of 2-AF in rat tissues in vivo.