The reduction of increased platelet aggregation in essential hypertension is one of the aims of modern antihypertensive therapy. Twenty-one hospitalized patients with non-treated essential hypertension were examined. The platelet function measurements were made before the therapy and after 1 week of celiprolol administration (300 mg/day). Fifteen essentially hypertensive patients were investigated before and after 1 week of placebo administration. Plasma β-thromboglobulin was assayed, and the whole blood platelet aggregation (initial and total – induced by adrenaline and ADP) was measured. A significant decrease in adrenaline-induced (from 19 to 13%, p < 0.02) and ADP-induced aggregation (from 15 to 13%, p < 0.05) was observed after celiprolol administration. This reduction of adrenaline-induced platelet aggregation may be explained by the stimulation effect of celiprolol on platelet β<sub>2-</sub> receptors. Thus, some inhibitory effect of celiprolol on platelet aggregation is one of the further advantages of this drug in the therapy of essential hypertension.