Problems of screening and surveillance programs for workers determined to be at risk of disease on the basis of epidemiological studies or industrial hygiene surveys are reviewed. Two categories of at risk workers can be discerned: The group undergoing the exposure at the time of risk assessment, and former workers or current workers with past exposures. Approximately 21,000,000 workers are now or have been exposed to federally regulated substances. Notification triggers a need for services including screening and medical surveillance. Problems with screening and surveillance in the case of cancer causing agents are discussed. A need for aggressive research in cancer detection and disease therapies is argued. Use of survival related indicators to evaluate the effectiveness of screening programs is considered important for a critical appraisal but is of limited usefulness in terms of the overall needs of groups at risk. For most, a screening program is an affirmation that they are still physically, well. The need for demonstrations of concern and various support services are pointed out. Initial motivation should be considered as one stage in a multistage process, using the information gained to update cohort surveillance recommendations and management. Problems of geographic distribution of the cohort are also considered. Screening and surveillance programs are recommended for gathering information on biological markers whose frequency may be altered by behavioral modification and chemoprevention programs. The ethical concern that identification of unvalidated markers may leave workers without a definitive interpretation of results is addressed. A strategy is proposed for research on biomonitoring in high risk groups. The importance of the social and political context in which screening and surveillance programs occur is considered, and guidelines are proposed.