To evaluate the incremental effectiveness of a work-site blood pressure control program, we conducted a randomized, controlled trial at four work sites with established health promotion programs. Workers with blood pressures of 140/90 mm Hg or higher were eligible. Eighty subjects were assigned to receive a referral to a community physician, monthly 10-minute work-site counseling sessions including blood pressure readings, and personalized mailings, whereas 79 control subjects received only a physician referral. Results for 74 intervention and 71 control subjects were obtained after 1 year. As compared with control subjects, intervention subjects experienced average declines of 8.5/3.9 mm Hg. Adjusted for age, sex, and baseline blood pressure, the decreases were 7.6 mm Hg for systolic and 2.4 mm Hg for diastolic blood pressure. These results suggest that counseling of high-risk persons and personalized mailing programs can have an incremental benefit in controlling blood pressure.