Lung function testing. among- occupationally exposed workers has demonstrated its usefulness in risk evaluation and, once risks are identified, in medical surveillance. Its usefulness for screening and biological monitoring for effects of exposure is not yet established; in part, this is due to some failure to understand the requirements for screening and for monitoring, and in part, it is due to some unresolved questions as to procedures and their interpretation. The use of screening in occupational groups in general and those exposed to inhala-tional risks is evaluated. The current recommendation is that priority for screening be given to risk factor reduction, including smoking cessation. Problems associated with screening relate to procedures, equipment, and interpretation of data.