Teniposide added to citrated platelet-rich plasma reduced platelet aggregation induced by collagen, but did not interfere with ADP-induced aggregation. The availability of platelet factor 3 was decreased irrespective of inducer. Reptilase clot retraction induced by ADP or collagen was reduced. Teniposide did not interfere with platelet adhesion to glass. It did not release lactic dehydrogenase from the cytoplasm of platelets. Coagulation factors were not affected.