During thrombocytophereses on a blood cell FENWAL CS 3000 separator in one group of donors the anticoagulant solution ACD-A recommended by the manufacturer was used, in the other group of donors ACD-A with heparin was used. The authors give an account of the changes in some parameters of haemostasis in these donors on the separator incl. examination of fibrinopeptide A which is the most sensitive indicator of clotting activity during separation. Heparin administration prevented a rise of fibrinopeptide A and did not lead to a reduced platelet yield.