Vanillin, capsaicin and chili extracts were tested for mutagenicity in Salmonella typhimurium histidine-deficient tester strains TA 98, TA 100, TA 1535, TA 1537, and TA 1538. Vanillin was nonmutagenic, whereas chili extract and capsaicin were mutagenic with metabolic activation. Capsaicin, an active component of chili extract, was the more potent mutagen. The positive samples were also tested in two mammalian test systems: the micronucleus test and the 8-azaguanine-resistant mutagenesis assay that used V79 Chinese hamster cells. It was observed that both were negative for the latter test at the dose level tested, whereas in the micronucleus test, only capsaicin was positive near the LD50 dose. Capsaicin also inhibited DNA synthesis in the testes of Swiss mice injected at two dose levels.