The effect of sulfinpyrazone on various parameters of platelet function was studied in volunteers. The shape change, adhesivity and aggregability of thrombocytes were significantly decreased after an oral treatment with 200 mg Anturano t.d.s. for seven days. Two days after the last medication this effect was still evident. In addition an experimental thrombosis was performed in rats by chilling a standardized segment of the carotid artery. After previous application of 10 and 100 mg/kg BW of sulfinpyrazone the thrombus formation was significantly decreased in comparison with the control group.