The etiology of occupational cancers is reviewed. Attention is focused on assay systems for predicting carcinogenesis and mutagenesis, on clinical recognition techniques for environmental and work related cancers, and on practical guidelines to interpret epidemiological studies. Methods of making risk assessments in formulating cancer policies are examined. While differences of opinion exist regarding the utility of various assay systems and the potential carcinogenesis of various substances, most scientists stress the need to improve current systems for data collection, analysis, and dissemination. Specific research goals are identified that include larger and more inclusive tumor registries, improved coding diseases in death certificates, follow up studies of occupational cohorts, and continuing education in occupational medicine for clinicians and health staff. Questions of clinical relevance concerning occupational and environmental cancers are examined. It is recognized that the explosion of scientific information on recognition, prevention, and control of cancer necessitates a high index of suspicion that occupational and environmental factors contribute to cancer.