Acebutolol and propranolol were compared in forty-five Black African patients in a double-blind randomized trial carried out at Ahmadu Bello University Teaching Hospital in Kaduna, Nigeria. After a wash-out period of 6 weeks, including placebo administration for the last 4 of those weeks, twenty-seven patients were given acebutolol once daily and eighteen were given propranolol twice daily for 12 weeks, followed by a tapering-off period of 2 weeks, making a total of 14 weeks on active treatment. The two beta-receptor blocking drugs were effective in controlling hypertension with final daily doses ranging from 160 to 320 mg in the propranolol group and 400 to 800 mg in the acebutolol group. The supine systolic blood pressure responses with acebutolol were statistically significant and better than those elicited by propranolol. Acebutolol produced less (resting) bradycardia than did propranolol; this may be related to acebutolol's intrinsic sympathomimetic activity. The only unpleasant side-effects reported in this study were slight dizziness in two patients treated with propranolol and slight tiredness in one patient treated with acebutolol. No significant abnormal changes were noted in laboratory tests or chest X-rays. Electrocardiography detected supraventricular tachyarrythmia in five patients: this disappeared by the end of the study. Acebutolol was shown to be a safe, effective and reliable antihypertensive drug, at least comparable to and probably slightly better than, propranolol in the treatment of hypertension in Black Nigerians. It has the added advantage of a once-daily dose schedule.