The deposition of platelets at the site of balloon angioplasty is thought to play a major role in the pathogenesis of restenosis. The antibody AZ-1, which binds to the rabbit platelet glycoprotein IIb/IIIa receptor and inhibits platelet function both in vitro and in vivo, was produced and tested in an experimental model of angioplasty. Atherosclerosis was induced by desiccation injury of the femoral artery, followed by a 28-day diet with 2% cholesterol and 6% peanut oil. Rabbits were randomized to receive an infusion of saline, a single infusion of 0.5 mg/kg of AZ-1, or an infusion of 0.6 mg/kg AZ-1 before angioplasty. The latter group received a second infusion of 0.6 mg/kg 72 hours later. Functional platelet inhibition was demonstrated by prolongation of the bleeding time in all treated animals. Angiography was performed at baseline, immediately after a standardized angioplasty, and again 28 days after angioplasty on a total of 42 vessels. There were no significant differences between the antibody-treated group and the control group in the mean angiographic minimum luminal diameter at any of the time points. There was also no difference in the initial improvement after angioplasty (acute gain), in the decrease in luminal diameter from immediately after angioplasty to 28 days after angioplasty (late loss), or in the overall improvement from before angioplasty to 28 days after angioplasty. Quantitative histological analysis confirmed the lack of a beneficial effect of AZ-1. There were no significant differences in the area of the intima, the media, or the combined intima and media between the antibody-treated groups and the control group. Thus, potent platelet inhibition for up to 6 days after balloon angioplasty using a monoclonal antibody that inhibits platelet aggregation did not reduce the response to vascular injury after balloon angioplasty in this rabbit model of experimental atherosclerosis.