Thermally-induced bacterial mutagens are formed when foods are processed by some commercial food preservation techniques. The processes which involve longer times and higher temperatures are most likely to produce mutagens (e.g., canning and evaporative concentration). Pasteurization and spray drying processes possess a low potential for creation of mutagens. The types of food products with the greatest tendency to contain mutagens following heat treatments are muscle foods such as canned meats and fish. Canned beef broth, chili, hash, roast beef, pink and red salmon, and mackerel contain substances which induce mutation rates up to 20 times higher than spontaneous revertant colonies in the Ames Salmonella mutagenicity assay. Using canned pink salmon as a representative product, reprocessing increased mutagen content, whereas addition of Maillard-browning reaction inhibitors led to significant decreases in mutagen formation. Even though thermally-induced mutagens can arise during household cooking (e.g., frying and charcoal grilling), the consumer can choose to minimize their production through use of lower temperature methods such as boiling, steaming or microwave heating. This option is not available to the consumer of commercially canned foods. Hence, further research into the reduction of mutagen formation during thermal processing is needed.