The hypothesis linking nitrate and increased risk of cancer rests on the proposition that nitrate is endogenously reduced to nitrite by bacteria and that carcinogenic N-nitroso compounds are formed. A large number of foods and biological material have been examined for their ability to generate mutagens or carcinogens under simulated gastric conditions in the presence of nitrite. Only a limited number of foods qualify under these conditions for consideration as potential sources of genotoxic agents. Foods that have generated mutagens following nitrosation include beans, salt-preserved fishery products, fermented soy products, and certain moldy foods. In each case there appears to be a potential link between formation of the nitroso compound and epidemiological evidence of increased risk for specific cancers. The present state of knowledge is reviewed and the chemistry of the nitrosation of specific chemicals of interest is discussed. A major problem for the future will be to demonstrate that these N-nitroso compounds form in the population at risk and react with cellular nucleophiles to produce genetic damage.