Twenty patients with mild to severe essential hypertension completed a 12-week open crossover study to compare the effectiveness and tolerance of two beta-blocker/diuretic combinations. Patients were allocated at random to receive treatment for 6 weeks with either 40 mg propranolol plus 12.5 mg hydrochlorothiazide twice daily or 400 mg acebutolol plus 25 mg hydrochlorothiazide once daily. They were then crossed over to the alternative medication for a further 6 weeks. Blood pressures and pulse rate were monitored in the supine and erect positions at regular intervals, as were side-effects, laboratory variables and ECG. The results showed that both combinations produced significant reductions from baseline in systolic and diastolic blood pressures but that the acebutolol combination produced a significantly greater reduction in diastolic blood pressure. There was no evidence of a treatment sequence effect. The two drug treatments were reasonably well tolerated, with a trend in favour of the acebutolol combination. No clinically significant changes were observed in any of the laboratory parameters investigated and there were no ECG abnormalities.