The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent pancreas carcinogen in rats. The biliary excretion of NNK was therefore studied in anesthetized female Sprague-Dawley rats following i.p. administration of 0.7 mumol/kg [carbonyl-14C]NNK. The concentration of radioactivity peaked within 30 min and decreased thereafter exponentially. Cumulative excretion of radioactivity reached a plateau at 6-9% of the total dose. HPLC analysis revealed the presence of 4-hydroxy-4-(3-pyridyl)butyric acid (hydroxy acid), 4-oxo-4-(3-pyridyl)-butyric acid (keto acid), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butyl beta-D-glucopyranosiduronic acid (NNAL Glu), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and NNK. NNAL Glu was the major metabolite contributing 34 +/- 4% of total radioactivity in bile at 30 min and 58 +/- 4% at 5 h. The percentage of acidic metabolites remained constant at approximately 20%. In contrast, the percentage of NNK and NNAL decreased within the first 2 h to < 5% and < 10% respectively. The elimination kinetics of NNK and its metabolites fitted into a one-compartment model with a half-life of 37 min for NNK, 52 min for NNAL and 110 min for NNAL Glu and acidic metabolites. In three rats dosed with 240 mumol/kg NNK i.p., the concentration of radioactivity peaked after 1-2 h and decreased very slowly thereafter. After 5-8 h a total of 12-17% of the dose has been excreted in the bile with no indication of a plateau. At all time points NNAL Glu was the major metabolite contributing up to 95% of total radioactivity in bile. The percentage of acidic metabolites was < 5% throughout the experiment. Whereas NNK contributed one-third of the radioactivity at 30 min and decreased rapidly, the percentage of NNAL in bile remained rather constant at approximately 5-10%. In conclusion, the detection of NNK, NNAL and NNAL Glu gives support to the hypothesis that tobacco-specific carcinogens could reach the pancreas retrograde from the bile, especially at high NNK concentrations.