Between April and December 1983 100 transluminal coronary dilatations in 98 patients were performed using new steerable balloon catheter systems. The primary success rate (diameter enlargement greater than 20%) overall was 87%, in stenoses of the anterior interventricular branch 88.1% (59 out of 67 interventions), in stenoses of the right coronary artery 88.9% (16 out of 18), and in circumflex branch stenoses 84.6% (11 out of 13). Within the first 50 interventions the success rate was 80%. Among the second 50 cases it was improved to 94%, mainly due to the increasing experience of the investigators. Emergency bypass operations had to be performed in two patients in whom coronary vascular occlusion had occurred. No patient died and in only one a small infarction occurred, probably due to occlusion of a side branch with an increase of creatine kinase to a maximum of 120 U/l. These figures show that steerable balloon systems clearly improve the primary success rate despite broadening of indications and diminish serious complications.