The challenges in cancer prevention for primary care health professionals are to apply effectively and efficiently the technologies that prevent disease occurrence and progression. The opportunity for providing preventive services in the medical care setting would appear to be potentially achievable, but it requires consideration of economic, organizational, and conceptual barriers. Studies of potential deterrents of optimal use of cancer screening tests have emphasized the leadership role of physicians. Physician advocacy of cancer screening guidelines or assigning priority to counseling about high-risk behaviors will be influenced by the critical and balanced presentation of scientific evidence on the safety and efficacy of preventive interventions. Chemoprevention refers to the use of pharmacologic or natural agents, currently under investigation, to prevent or delay the development of cancer in ostensibly healthy persons with specified risk factors or precancerous conditions.