Computer-assisted quantitative angiographic analysis was undertaken of 17 stenoses in aortocoronary bypass vessels in 14 patients. Angioplasty was successful in 13 of 17 haemodynamically significant bypass stenoses, with a reduction in the degree of stenosis (cross-sectional reduction) from 82 +/- 9% to 44 +/- 9% (P less than 0.001) and a significant reduction in flow-related stenosis resistance. This method revealed significant bypass restenoses in 38% within 9 +/- 6 months, successfully treated by a second angioplasty. These patients make up a group which--in contrast to the natural progression of vascular sclerosis--is characterized by an early development of bypass stenoses and restenoses. Transluminal angioplasty after stenoses and restenoses in bypass vessels is an effective and safe alternative to reoperation.