Work-related disease is the product of multiple factors, including host susceptibility, the external environment, and individual behavior. The concept of multiple causality is relevant to the etiology of diseases, in which work and exposures are contributory agents, and of diseases that have a single necessary cause, eg, lead poisoning. The objectives of medical screening in the control of work-related diseases are the subjects of this paper. Screening procedures include questionnaires, diagnostic tests, function measurements, and biological tests of exposure levels to environmental agents. Achieving the objectives of medical examinations depends on (1) selecting appropriate tests that are acceptable to workers; (2) discarding tests that cannot meet requirements with respect to reproducibility, specificity, and sensitivity; and (3) periodically reviewing health surveillance programs as a whole, and modifying or abandoning them as necessary in the light of improved working conditions