Sixty patients in whom a prosthetic aorto-femoral bypass graft was inserted were pretreated with ticlopidine (250 mg b.i.d.) or placebo in a double-blind study. Blood loss and transfusion need were higher in ticlopidine treated patients. Platelet survival was partially corrected and platelet deposition on prosthetic surfaces was inhibited with ticlopidine. The study suggests that ticlopidine does not increase excessively the bleeding risk during peripheral vascular surgery and that the antiplatelet drug may have beneficial effects in the early phase after insertion of prosthetic vascular graft.