Among all establishments perceiving a change as a result of their medical surveillance program, 43% of those employing 250 or more employees did so; for the smallest establishments, this figure drops to 7%. The changes most often perceived, regardless of size class of establishment or industry division, were in employee relations, injury rates, and insurance costs. Establishments with the most comprehensive risk reduction strategies were most likely to attribute benefits to their medical surveillance programs. Benefits of medical surveillance perceived by the Phase II respondents include reduced costs, early detection of medical problems, increased productivity, and a reduced injury or illness rate. Most firms have no systematic method or procedures for evaluating the effectiveness of their medical surveillance programs.