Platelet functions and blood clotting parameters were examined in 23 patients with a shortened platelet survival time after cardiac valve replacement. Treatment was given at random: for a first group antivitamin K with suloctidil and for the second group antivitamin K alone. Six weeks of treatment with antivitamin K alone did not induce any significant change in the platelet survival time, platelet retention or platelet factor 4 in plasma. In contrast, the shortened platelet survival time increased significantly after 6 weeks of treatment with suloctidil. Moreover the platelet retention and the amount of platelet factor 4 in plasma were significantly reduced, indicating that normalization of platelet survival is the result of decreased destruction, presumably at the level of the prosthetic surface. The clinical benefits expected from these results remain to be validated by a longer follow up period.