In Ames test, the quinoline derivatives, 6-nitroquinoline (6-NQ), 8-nitroquinoline (8-NQ), 6-methylquinoline (6-NQ), 8-methylquinoline (8-MQ) and 8-hydroxyquinoline (8-HQ) are mutagenic, whereas 5,7-dibromo-quinoline (5,7-DQ) is not. These compounds were administered to groups of male and female F344 rats in their diet for 104 weeks. 8-NQ induced forestomach tumors in male and female rats: it induced squamous cell papillomas in 28 (93.3%) of 30 males and in 36 (97.3%) of 37 females, and squamous cell carcinomas in 20 (66.7%) of 30 males and 24 (64.9%) of 37 females. Thus there was no sex difference in its carcinogenicity. 6-NQ induced only focal hyperplasia of the forestomach at an incidence of 30.0% in male rats and 52.8% in female rats. These results indicate a discrepancy between the mutagenicities of quinoline derivatives and their carcinogenicities to rats: only 8-NQ was carcinogenic to F344 rats.