The International Agency for Research on Cancer has initiated a program to evaluate the carcinogenic risk of chemicals to man. This program is centered on the production of monographs on individual chemicals, consisting of data on use and production, carcinogenicity in experimental animals, epidemiological studies and case reports, and other biological data such as metabolism and mutagenicity, and ending with a balanced evaluation of all the data made by an international group of experts. Chemicals to be surveyed for the preparation of monographs have so far been selected among those for which some evidence or suspicion of carcinogenicity in experimental animals and/or man exists and for which human exposure is known to occur. Of the 196 compounds already evaluated, 17 have been found to be associated with cancer in man. Ninety-four compounds were definitely carcinogenic in experimental animals, and 41 were shown to have a limited carcinogenic effect in experimental animals. A number of the chemicals found to be carcinogenic in experimental animals are produced in very large quantities. The type of exposure to the 17 chemicals found carcinogenic to man was occupational for fourteen, medicinal for two, and dietary for one.