Carcinogens occur naturally in the foods we eat, including a number of HCAs that have been identified in foods (beef, pork, poultry and fish) as a result of cooking. These compounds are formed during the normal cooking process by the reaction of creatine with various amino acids. The HCAs have been identified as a result of their high mutagenic activity in the Ames test. The HCAs can be separated into two types, the nonimidazole and the imidazole type, the latter of which is the predominant type present in Western foods. Both types of HCAs have been found to be carcinogenic in rodent bioassays. Of the three imidazole compounds presently under evaluation in nonhuman primates, IQ has been found to be a potent carcinogen, inducing hepatocellular carcinoma in a majority of the animals in approximately one-seventh of their life span. In addition, a high proportion of the nonhuman primates also had focal IQ-induced myocardial lesions as observed by both light and electron microscopic findings. This information, along with other toxicology data on the HCAs, much of which is cited in this paper, allows the inference to be made that HCAs may be a risk factor for both cancer and cardiovascular disease in humans.