Randomized, double-blind. Eighty-three patients (90 endarterectomies) were randomly assigned to receive 325 mg of oral aspirin plus 75 mg of dipyridamole, beginning 12 hours pre-operatively, followed by a second dose administered within eight hours after the operation, and given three times daily thereafter for one year. Eighty patients (85 endarterectomies) received placebo. After the adequacy of the surgical procedure was confirmed by intraoperative angiography, restenosis at the endarterectomy sites was evaluated using serial duplex ultrasound before hospital discharge and at three-month intervals postoperatively for one year.