[en] Injury to the vascular intima reslts in smooth-muscle cell (SMC) proliferation of the newly-forming intima and is regarded as first event in the development of atherosclerosis and reocclusion of the vessel. Mechanically deepithelialized rat aorta and a jugular vein graft shunting the carotid artery in dogs were employed as models in this study. The rat aorta was purufied from the endothelium with a ballon catheter. Irradiation of the rat peritoneal aorta in doses of 700 to 1500 sGy prevented SMC proliferation in the intima that formed after the injury inflicted with ballon. Similar inhibition of SMC proliferatin was seen in the neointima of venous grafts irradiated in vitro in doses of 1500 to 2000 sGy