Our study evaluates the equity and efficiency of OSHA enforcement relating to the nature of the firm, the intensity of the inspection, and the size of penalty, based on the experience of 6,842 firms between 1979 and 1985. We found that: (1) enforcement actions against firms with one hundred to five hundred employees had greater general and specific deterrence effects than against larger or smaller firms; (2) superficial inspections that checked only the firm's injury records were ineffective. Health inspections, which tend to be more intense, also reduced injuries, but repeated inspections in the same year did not; and (3) larger penalties did not increase either general or specific deterrence. Small penalties decreased injuries as much as larger ones, and took considerably less inspection time. We discuss implications for policy, and emphasize the need for further research on the equity and efficiency of enforcement.