Thirteen patients with advanced hypertensive disease insufficiently controlled by conventional drugs were treated with minoxidil in combination with a beta-blocking agent and a thiazide in a long-term study. A reduction from 214 +/- 5/122+/3 to 166 +/- 7/95 +/- 3 mm Hg in the mean supine blood pressure was obtained. The dosage range of minoxidil was 7.5-35 mg per day (mean 18.8 mg), and in all cases beta-blockade was necessitated by the occurrence of reflex tachycardia. Only two of the patients were found to be unsatisfactorily controlled on combined therapy. In five cases, minoxidil was disontinued during the observation period, but only in three cases was the discontinuation due to side effects, v.z. sodium retention and augmented hair growth. Stable diabetes developed in one patient, and in two cases of established, dietetically treated diabetes oral antidiabetic drugs had to be administered. Five non-diabetic patients showed no significant changes in fasting plasma glucose and the K values in intravenous glucose-tolerance tests. Minoxidil seems to be a safe and potent antihypertensive drug for long-term use in severe arterial hypertension, but it cannot be recommended for routine treatment.