The authors administered to 10 patients with mild hypertension a single dose of 10 mg bisoprolol (Concor-Merck) during bioimpedance control of changes of the cardiac index and peripheral vascular resistance after an interval of 3 and 24 hours following administration of the drug. In all patients administration of the drug led to a statistically significant drop of the blood pressure. In patients with a high cardiac output (group A, n = 6) the decline of blood pressure was due to a blocked increment of the cardiac output and a slight block of the peripheral vascular resistance. In the group with a low cardiac output and high peripheral vascular resistance (group B, n = 3) the drop of the blood pressure was caused by peripheral vascular dilatation, the cardiac output was influenced minimally. Bisoprolol did not affect the left ventricular systolic function.