The distribution of medical screening practices in United States private industry was investigated. Data from 4500 workplaces surveyed by NIOSH from 1972 to 1974 (survey 1) and from 1981 to 1983 (survey 2) were employed. Data from personal interviews, questionnaires, and walk through surveys were analyzed. Preplacement examinations were given to 47.7 percent of workers in survey 1 and 58.8 percent in survey 2; periodic medical examinations increased from 33.7 to 40.2 percent over this period. Overall, workers in production facilities with more than 500 workers were approximately four times more likely to be given these examinations than workers in facilities with less than 100 employees. In survey 1, chest radiographs were most commonly provided, followed by ophthalmologic and audiometric tests. Less than 15 percent of workers were given blood, urine, or pulmonary function tests. Ten years later, the percentage of workers given these tests increased, with greatest increases in radiographs and ophthalmic testing. Workers in transportation and public utilities were most likely to have screening examinations, while those in contract construction were least likely. In survey 2, approximately 50 percent of the workforce were employed where environmental monitoring was conducted, compared with 33 percent in survey 1. Examination of workers exposed to selected toxic chemicals showed workers at facilities employing 500 or more were 3.5 to 19 times more likely to have medical examinations than workers in small or medium facilities. Only 27.8 percent of workers potentially exposed to dusts had periodic chest radiographs and 17 percent pulmonary function tests while approximately 14.5 percent of workers potentially exposed to heavy metals received blood or urine tests. The authors conclude that, although screening practices have increased, factors other than hazardous exposures are major selection determinants, and guidelines for occupational screening are necessary.