The therapeutic advantage of the long acting ACE-inhibitor benazepril in a 12 weeks intervention period on 23 diabetic (3 IDDM, 20 NIDDM) patients with essential hypertension was studied. Participants-giving informed consent before beginning the study-on the base of repeated casual blood pressure measurements were divided into "slightly" (n = 8) and "moderately" (n = 15) hypertonic groups. Type of diabetes, time elapsed since its manifestation, actual antidiabetic therapy, period of existence of the hypertension (newly discovered vs known and treated for a time) were independent from the point of view of entering the study. Initial dose of benazepril was 5-10 mg/day depending on the blood pressure level, followed by a stepwise dose elevation according to the control investigations (at weeks 2, 4, 8 and 12 casual blood pressure control, at weeks 4 and 12 ambulantory blood pressure monitoring, ABPM as well) to a maximal daily dose of 20 mg. In the majority of patients benazepril was given in a morning single dose, in some cases because of a better tolerability divided into two parts. 20 patients received benazepril in monotherapy, 3 patients combined with other antihypertensive preparations. Parameters indicating severity of hypertension-hypertonic time index, hyperbaric impact-showed significant improvement already at week 4 when analysed in the total of patients and the moderately hypertonic group respectively. As a tendence the same was observed also in the slightly hypertonic group. No remarkable side effects, or alterations of the metabolic state and in the investigated laboratory parameters appeared. Based on these results benazepril is an effective choice in the treatment of diabetic hypertensive patients.