The early and late effects of a new balloon-expandable coronary stent (Boneau II) were studied in 16 adult mongrel dogs. Thirty-three balloon-expandable stents were deployed using standard transfemoral coronary angioplasty technique. Single stents were placed in eight dogs and multiple (two to four) stents were placed in eight dogs. Intravenous heparin (3,000 units) was administered at the beginning of the procedure. Aspirin, dipyridamole, dextran, and warfarin were not administered before or after the procedure. All stent deployments were successful. Angiographic or pathologic examinations were performed within 24 hr of deployment on two of the dogs, at 2 weeks on two of the dogs, at 2 months on three of the dogs, at 6 months on six of the dogs, and at 1 year on three of the dogs. All successfully deployed stents were noted to be widely patent. There was no evidence of side-branch vessel occlusion. There was no evidence of acute or late vessel thrombosis. Histologic examination at 2 months showed a mean intimal thickness of 153 microns. The stainless steel Boneau II coronary stent is relatively short and easily deployed. This balloon-expandable coronary stent was successfully deployed in normal canine arteries without the use of anticoagulation or antiplatelet therapy before or after the procedure. The Boneau II intracoronary stent has a very low thrombogenic potential in dogs.