The baboon offers many advantages as an experimental animal to study vascular disease, thrombus formation and dissolution, effects of mediating variables, and the relative efficacy of therapeutic interventions. Each specific application for testing therapeutic agents may require testing in somewhat different model systems. For example, although the arteriovenous vascular graft model is efficient, cost effective, and well adapted to study of interventions for acute arterial thrombosis, surgical endarterectomy extends the evaluation to include interactions with the injured vascular wall. As the antithrombotic products of genetic engineering and molecular biology emerge, it will be increasingly important to have relevant, reproducible, and quantitative approaches to evaluate their effects in vivo.