The objective of our work is to obtain information on the nature of the chemical carcinogens which may be ingested as part of the diet. Various epidemiologic studies have suggested that dietary factors, particularly high dietary fat and beef, are of major importance in the etiology of cancer of the colon. A two-stage model has been suggested wherein the combined action of carcinogens and promoters are necessary for the development of large bowel cancer. The ability of high dietary fat to induce increased excretion of bile acids has been shown to be related to the promotion of tumors in the colon. The initiating agent remains unknown, but epidemiologic evidence has implicated broiled meat. Several groups have reported mutagenic activity in meat cooked either by charcoal broiling or by frying. Nagao et al. noted that the mutagen is formed during pyrolysis of protein. Commoner et al. suggested that a critical temperature of 150-200 degrees C must be passed before the mutagen forms. Since this temperature range is not reached in broiling, he concludes that this mode of cooking is "safe". We demonstrate that all modes of cooking have the potential to produce mutagenic material and are isolating the mutagens in order to assay their carcinogenicity.