The results of 126 consecutive balloon dilatations of coronary arteries, carried out in 110 patients between 1980 and the end of 1983, are reported. The follow-up periods ranged from one to 47 months. The primary success rate was 74%, and the long-term success rate was 65%. In successful cases, the diameter of stenosis was changed, on average, from an initial 88% to 33%. Acute occlusion of the vessel occurred on 13 occasions (10%). Of these, myocardial infarction occurred in eight (6%), and emergency bypass grafts were performed in nine (7%). One of these 13 patients died (case fatality rate, 0.8%). Occlusion of the dilated vessels did not occur after the patients were discharged from hospital. However, stenosis recurred in 20 of 80 patients with successfully dilated arteries (25%). Dilatation was repeated in 16 of these, and stenosis had not recurred at the three-months' follow-up. There has been a marked improvement in the success rate of this procedure over the years. It is concluded that balloon dilatation is an effective and safe alternative to bypass graft surgery in selected patients with coronary artery disease.