Bopindolol (LT 31-200), a new, long-acting, nonselective beta-adrenoceptor blocking agent with partial agonist activity, was given to 23 patients with essential hypertension (World Health Organization stage I-II), aged 19-59 years, for 12 weeks. Four patients had low, 13 patients normal, and six patients high plasma renin activity (PRA). Bopindolol, once daily, was started at 1 mg and, when necessary, increased to 2 and 4 mg at intervals of 2 weeks, aiming at a diastolic blood pressure less or equal to 95 mm Hg. Blood pressure was reduced from 151 +/- 12/105 +/- 7 during placebo to 129 +/- 10/88 +/- 6 after bopindolol treatment, at a mean dosage of 2.4 mg. Heart rate decreased slightly from 75 +/- 7 beats/min during placebo to 71 +/- 10 beats/min during bopindolol treatment. A diastolic blood pressure less than or equal to 95 mm Hg was achieved in 19 of the 23 patients. The diastolic blood pressure decrease was greater in the eight patients aged 19-35 years than in the 15 patients aged 36-59 years. The decrease in diastolic blood pressure was also greater in the 19 patients with normal or high PRA than in the four patients with low PRA. PRA decreased from 2.6 +/- 1.7 micrograms/L/h, during placebo, to 1.6 +/- 0.8 micrograms/L/h, after bopindolol treatment, as measured in 19 patients. Plasma catecholamine levels were not changed after bopindolol treatment, as measured in 10 patients. Bopindolol was generally well tolerated, and all patients completed 12 weeks of treatment.