A number of related heterocyclic amines that are mutagenic in bacterial test systems and carcinogenic in animals are formed during the cooking of food. The most commonly reported and abundant compounds are PhIP, MeIQx, DiMeIQx, IQ and A alpha C. Using analysis by solid-phase extraction and HPLC, amounts found in foods range from less than one ng/g for products from fast-food restaurants, up to 14 ng/g in commercially cooked products and over 300 ng/g for well done flame-grilled chicken breast meat. Interestingly, marinating meat for 4 h greatly reduces the amount of PhIP produced during cooking, but not MeIQx. Comparing mutagenic activity in meat samples to the mutagenic activity accounted for by the known heterocyclic amines shows that most samples have activity that cannot be accounted for by the aromatic amines we can currently identify. This suggests that additional compounds are present in these foods and need to be investigated, particularly those grilled over open flames.