The efficacy and safety of daily 20 mg betaxolol monotherapy was investigated in mild-moderate essential hypertension in a four week long, open label, single blind trial (with a placebo run-in). Twenty one patients of both sexes were enrolled. The systolic blood pressure in the supine position decreased from 158 to 142 mmHg, the diastolic blood pressure from 101 to 89 mmHg. The mean systolic values of the 24 hours ambulatory blood pressure monitoring decreased from 136 to 126 mmHg, the mean diastolic values from 87 to 80 mmHg. All decreases in blood pressure were significant. The reduction of the heart rate (80/min vs 63/min) was also significant. The decrease in blood pressure during daytime was significant, during night it was moderate. The blood pressure- and heart rate reducing effect of betaxolol was detectable however in the second half of the night, before wake-up. No side effect was recorded.