This double-blind, placebo-controlled, randomized multicenter study evaluated the antihypertensive efficacy and safety of cetamolol hydrochloride in 108 patients diagnosed as having mild to moderate hypertension. After a placebo lead-in period, patients received either cetamolol 5-10-15 mg/d (low dose), cetamolol 15-25-50 mg/d (high dose), or placebo, once daily for four weeks. Patients began at the lowest dose and were titrated to higher doses based on the first two assessments of diastolic blood pressure and heart rate, which were conducted each week after double-blind treatment was dispensed. After four weeks of treatment 82.4%, 81.3%, and 93.3% of the low-dose group, high-dose group, and placebo group, respectively, were titrated to the maximum dose level. After four weeks of treatment and 24 hours since the patient's last dose, both cetamolol groups showed a significantly greater (P less than or equal to .05) reduction in supine systolic/diastolic blood pressure (-18.1 +/- 2.3/-9.2 +/- 1.5 mm Hg [low dose] and -17.3 +/- 2.3/-8.3 +/- 1.6 mm Hg [high dose]) than the placebo group (-9.9 +/- 2.5/-3.5 +/- 1.7 mm Hg). In general, the changes in standing (stabilized) systolic and diastolic blood pressure were similar to those seen in supine measurements. Significantly more patients receiving cetamolol than those receiving placebo showed a "good response" (a decrease in diastolic blood pressure of 10 mm Hg or more or measuring less than 90 mm Hg with a decrease of at least 4 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)