A randomized, double blind clinical trial included 40 hypertension patients of both sexes, aged 18-70 years, with diastolic blood pressure persistently above 100 (13.33 kPa) and below 120 mm Hg (15.99 kPa). After a run-in period on placebo, one half of them was treated with bopindolol (single daily dose 1-3 mg), and the other half with metoprolol (100-300 mg daily in two divided doses). After 4 weeks of formal trial both beta blockaders had significantly decreased the elevated arterial pressure, e.g. the mean arterial pressure in the bopindolol group dropped from an average of 129.1 +/- 6.9 (17.20 +/- 0.92) to 111.6 +/- 6.1 mm Hg (14.87 +/- 0.81 kPa) or by 13.6% and in the metoprolol group from 129.8 +/- 7.1 (17.30 +/- 0.94 kPa) to 114.5 +/- 6.4 mm Hg (15.26 +/- 0.85 kPa) or by 11.8% (p less than 0.02). After 12 weeks the mean pressure was ulteriorly lowered to some 104.3 mm Hg (13.90 kPa) on bopindolol and to some 106.0 mm Hg (14.12 kPa) on metoprolol. The heart rate was expectedly slowed down, from an average of 95 to 69 b.p.m. with bopindolol (27.4% decrease, p less than 0.001) and from 99 to 67 b.p.m. with metoprolol (32.3% decrease, p less than 0.001). The other parameters, including the laboratory results did not change appreciably during this study. Clinically relevant side-effects were not registered, and the observed between-group differences did not reach the level of statistical significance. It is concluded that bopindolol and metoprolol are beta-adrenergic blockaders of comparable antihypertensive efficacy.