The efficacies of the non-steroidal, anti-inflammatory drug sulindac and the schistosomicidal agent oltipraz in inhibiting lung tumorigenesis was measured in A/J mice. Lung tumors (15.7 tumors/mouse) were induced by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK; 9.1 mg/mouse) administered in drinking water for 7 weeks. Feeding mice with sulindac (123 mg/kg diet), 2 weeks before carcinogen treatment until they were killed reduced tumor multiplicity by 53%. Oltipraz (250 mg/kg diet), however, has no effect on tumorigenesis. The absorption and metabolism of NNK were compared in the stomachs and intestines isolated from mice fed AIN-76A diet or sulindac + diet. Sulindac had no effect on alpha-carbon hydroxylation, pyridine N-oxidation or carbonyl reduction of NNK. Mouse lung explants were cultured with 4.7 microM [5-3H]NNK for 4 or 8 h. The addition of 1 mM sulindac to the culture medium reduces the alpha-carbon hydroxylation and pyridine N-oxidation of NNK. However, the administration of sulindac in the diet prior to the excision of the lung explants had no effect on these two metabolic pathways. We compared the levels of sulindac and its sulfide and sulfone metabolites in the lungs, livers and plasma of mice fed an AIN-76A diet containing 130 mg sulindac/kg for 2 weeks. The sulfide metabolite was the most abundant of the three compounds in plasma (17.6 pmol/microliters) and liver tissues (17.7 pmol/mg) but it could not be detected in lung tissues. These results show that non-steroidal anti-inflammatory drugs constitute a new class of chemopreventive agents in lung tumorigenesis. The tumor chemopreventive activity of sulindac is not mediated by the sulfide metabolite responsible for its anti-inflammatory activity.