Undesirable changes of haemostasis induced by some anti-hypertensive drugs can encourage the acceleration of atherogenesis. Therefore, the changes of haemostasis parameters in 22 patients with essential hypertension under long-term celiprolol therapy (> 2 months) were of interest. In the placebo group of 15 essentially hypertensive patients there were no significant changes in platelet activity. On the other hand, the therapeutic dose of celiprolol was shown to reduce total platelet aggregation, without any harmful effects on fibrinolytic activity and coagulation inhibitors such as protein C and antithrombin III. The metabolic neutrality of celiprolol accompanied by the proven platelet-inhibitory tendency is desirable in the new approach to hypertension treatment. Potentially anti-thrombotic or at least neutral prothrombotic properties of celiprolol may be important in terms of the favourable role of anti-hypertensive drugs in cardiovascular morbidity.