A worksite-based program to detect and provide long-term treatment for working persons with high blood pressure was begun in 1973. In this setting, systematic categorical care, provided primarily by nurses under physician supervision, is effective, acceptable, and produces a reduction in cardiovascular morbidity and mortality when compared to conventional community-based care. The existence of a large, stable, treated group drawn from a defined working population has also provided an unusual opportunity to pursue clinical epidemiological research requiring prolonged prospective study. Issues of patient management, the course of clinical disease, and more fundamental biological research, have all been successfully addressed in this setting. The worksite may, therefore, present a useful opportunity for the investigation and treatment of other common chronic diseases.