The authors follow up the effectiveness and tolerance of monotherapy with acebutolol in 47 patients with light and moderate hypertension, in a dose of 400-1200 mg in the course of three months. Twenty two of the patients have been treatment with the original French drug of the firm "Specia" and the rest 25--with the Bulgarian preparation, produced by Pharmachim according to a licence of the French one. The following parameters were followed up: arterial pressure, pulse rate, ECG, eventual adverse effects on 30, 60, 90 day of the treatment. The indices of cardiac output and total peripheral vascular resistance were calculated in a group of 13 patients. The results obtained reveal that the monotherapy with acebutolol, in light and moderate arterial hypertension, leads to definite, lasting and progressive antihypertensive effect in over 75% of the patients. The preparation has no significant effect on pulse rate and induces no orthostatism. It affected the total peripheral vascular resistance with 26% from the initial with unchanged or lightly increased indices of cardiac output. The Bulgarian drug, produced by Pharmachim, gives no way in effectiveness to the original French preparation.