OBJECTIVE: To assess the short-term efficacy and safety of metoprolol in the treatment of hypertension in a large population of older patients. DESIGN: Prospective, open-label surveillance study. SETTING: Multicenter outpatient offices. PARTICIPANTS: 21,692 patients with mild-to-moderate hypertension between the ages of 50 to 75 years. Patients were excluded if they had a contraindication to beta-blocker therapy. INTERVENTION: Patients were treated with 100 mg of metoprolol once daily for 4 week. If the blood pressure was controlled, therapy was continued for an additional 4 weeks. If adequate blood pressure was not achieved after 4 weeks, 25 mg of hydrochlorothiazide was added. At the end of 8 weeks, final therapy decisions were recorded. If the blood pressure was controlled, therapy was continued for an additional 4 weeks. MAIN OUTCOME MEASURES: Blood pressure, heart rate and side-effects. RESULTS: After 4 weeks of therapy, mean systolic and diastolic blood pressures decreased significantly from 162/95 to 148/87 mm Hg (P less than 0.001). Fifty-eight percent of the patients had satisfactory blood pressure control. At the end of 8 weeks, mean systolic and diastolic blood pressure decreased to 143/84 mm Hg. Blood pressure response was similar in all age groups. At the termination of the study, 50% of the patients were continued on monotherapy, and 27% were continued on combined therapy. Overall, there was less than a 5% incidence of medical problems, and excellent or good tolerability was noted for 94% of the patients. CONCLUSIONS: Metoprolol administered as monotherapy or in combination with hydrochlorothiazide was effective in normalizing blood pressure in a majority of elderly hypertensive patients. Both drug regimens were well tolerated.