Effect of antiplatelet treatment on deposition of platelets (□) and fibrin (▪) on collagen-coated coverslips evaluated by immunoenzymology. The surface was exposed for 3 minutes to nonanticoagulated blood at a shear rate of 2,600 s⁻¹ from volunteers given either aspirin (ASA), ticlopidine (T), or the combination of both (ASA + T) or placebo (P). Values are means ± SEM (n = 16). *P < .05, **P < .01 versus placebo.