Repeat angiography was performed after 3-4 months in 927 of 1386 consecutive patients (67%) who had a successful percutaneous coronary angioplasty (PTCA) between 1986 and 1988. The degree of coronary artery stenosis was determined angiographically before PTCA, immediately after and 3-4 months later. Patients were assigned to one of four groups according to balloon diameter at dilatation: Group 1: 1.5-2.0 mm; group 2: 2,5 mm; group 3: 3.0 mm; group 4: 3.4-4.2 mm. Vessel wall proliferation occurred in all four groups after PTCA. In patients with angiographically demonstrated recurrence (first recurrence: 308 patients, second recurrence: 43 patients) another balloon dilatation was undertaken and a repeat angiography 3-4 months later. Long-term success rate (less than 50% stenosis) differed significantly according to the post-PTCA vessel diameter: 48% in group 1, 63% in group 2, 66% in group 3 and 80% in group 4 (analysis of variance: P less than 0.001). PTCA thus produces better long-term results in large than in small vessels.