Percutaneous transluminal dilatation (PTD) of coronary stenosis is performed by means of a balloon-tipped catheter introduced from a peripheral artery. PTD was attempted in 56 patients; stenosis was successfully dilated in 38 patients (68%). The method failed in 18 patients: in 6 (11%) of them an abrupt closure of the stenosed artery or a beginning infarction necessitated an emergency revascularization. There were no serious complications or deaths; one patient developed a transmural infarction in spite of the immediate bypass grafting. PTD was also successful in 6 out of 9 patients with recurrent angina following previous coronary bypass grafting. Intraoperative dilatation by coronary arteriotomy was attempted in 6 patients, but the results were inconclusive. PTD is a new method of treatment of coronary artery disease; it represents an addition rather than an alternative to coronary bypass grafting. The decision for PTD should be made jointly by cardiologist and surgeon; the ideal patient has a short history of angina with narrow, proximal stenosis without any calcifications. Cardiosurgical standby is mandatory during PTD; the results are best and the risk lowest in patients with single vessel disease.