The effects of 45 mg pindolol daily on blood pressure, heart rate, plasma renin activity, and plasma catecholamines were assessed on 11 hospitalized hypertensive patients. Blood pressure decreased significantly after nine days of treatment, but heart rate remained unchanged. Plasma renin activity was in the same average range before and during treatment, with individual values variably increasing, decreasing, or remaining unchanged. Blood pressure changes were independent from the baseline level of plasma renin activity or the change in renin activity observed during treatment. Plasma epinephrine and norepinephrine levels also remained unchanged during treatment. Lack of change in heart rate and hormonal levels may be attributed to the combined effects of the beta-antagonistic and partial agonistic properties of this agent. Thus, pindolol used as monotherapy at this dose significantly lowered blood pressure, but not to normal levels, with only minimal side effects. Because of its combined adrenergic agonistic and antagonistic effects, it may be a preferable alternative to pure antagonists in selected patients.