In order to assess the importance of physical accessibility in the efficacy of a union-sponsored, worksite-based hypettension detection and treatment program, the experience of patients offered identical systematic treatment in worksite and non-worksite settings was compared. Although attrition was greater in the offsite clinic in the first year, the difference disappeared by the second year. Successful blood pressure control was maintained over three years in both treatment sites. These results suggest that physical accessibility was not the sole or even the most important factor producing favorable results in this program. Other factors such as protocol-directed treatment by nonphysicians, the categorical nature of the program, lack of cost, and a socially cohesive work community may singly or together be factors responsible for successful therapy.