Shamma, a complex mixture of powdered tobacco, slaked lime, ash, oils, spices and other additives, has been linked to oral cancer in Saudi Arabia. Shamma varies in colour and odour due to the nature of the additives which characterize different brands. Using the Ames Salmonella assay, a chloroform extract of a brand named 'white shamma' (WSH) was found to be mutagenic, while that of a brand called 'brown shamma' (BSH), which is known to contain mint as a flavouring agent, was found to be non-mutagenic. Using HPLC, a mutagenic and a non-mutagenic fraction were isolated from the extract of BSH. The non-mutagenic fraction of BSH was found to neutralize the genotoxic effect of the mutagenic fraction when the two were recombined. A chloroform extract of mint showing no mutagenic activity in the Ames assay effectively inhibited the mutagenicity of carcinogens/mutagens like benzo[a]-pyrene, aflatoxin B1, methylmethane sulfonate and extract of WSH. A carcinogenicity assay designed to test the effects of WSH and BSH in the hamster cheek pouch model showed that the former was tumorigenic, while the latter was not. However, when crushed leaves of mint were mixed with powdered WSH (in 1:1 proportion), the tumorigenic effect of the latter was abolished. These data strongly suggested that mint has a chemopreventive effect against shamma-induced carcinogenesis, which could be due to its antimutagenic properties.