Fifty patients submitted to thromboendarterectomy in the femoropopliteal district for obstructive arterial disease of the lower limbs, documented angiographically, were randomly allocated to treatment with ticlopidine (500 mg/day) (T) or a placebo (P) in double-blind conditions. The treatment was started as soon as possible after the surgical intervention and was continued for six months or until a clinically evident reocclusion occurred. There were 46 patients available for assessment, 23 in each treatment group both of which were comparable in preoperative characteristics and type of surgery. Doppler ultrasonography at the end of treatment showed three cases of reocclusion of the operated segment in the T group versus six occlusions and seven significant stenoses in the P group (p = 0.003). Clinically, the active treatment significantly reduced the incidence of both acute ischemia during the treatment (four cases, all in the P group) and residual claudication at the end of treatment: in the T group five patients presented persistent or recurrent symptoms versus 16 in the P group (p = 0.001). Hemostatic function tests showed a marked inhibition of platelet activation in the T group. The treatment was well tolerated.