In order to assess the medium-term efficacy of ketanserin in comparison with that of the beta-blocker, propranolol, a randomized double-blind crossover trial was conducted involving 13 patients suffering from mild or moderate essential hypertension. Six of these patients were also evaluated on an ambulatory basis using noninvasive intermittent blood pressure monitoring to corroborate these values. Results indicated that both ketanserin and propranolol significantly lowered systolic, diastolic, and mean blood pressure levels after 60-day treatment periods. Diastolic blood pressure levels of less than or equal to 90 mm Hg were achieved in seven patients following ketanserin therapy and in six patients after treatment with propranolol. Both ketanserin and propranolol reduced arterial blood pressure without interfering with its circadian rhythm and variability. A tendency for the blood pressure lowering effect of ketanserin to increase with age was also noted. Side effects were minimal. The results of this trial confirm the efficacy and safety of ketanserin for the treatment of mild or moderate hypertension.