This study evaluated the frequency of coronary angioplasty of non-significant (< 50%) stenoses during procedures of multiple revascularisation, and also determined the angiographic outcome of these dilatations at 6 months. All coronary lesions were assessed by quantitative angiography before and after angioplasty and at the 6 month control examination. In a population of 696 patients undergoing angioplasty of at least two coronary segments, 29 had a stenosis of < 50%. Angiographic control at 6 months was obtained in 26 of these patients (90%), corresponding to 61 coronary stenoses 29 of which were not significant (< 50%) (Group 1), and 32 of which were significant (Group 2) before angioplasty. By definition, before angioplasty, the lesions in Group 1 were less severe than in Group 2 (41.8 +/- 6.6% versus 65.9 +/- 9.6% respectively, p < 0.0001). After angioplasty, the degree of stenosis was comparable in the two groups (30.7 +/- 9.4% and 33 +/- 10.4%). At the 6 month control angiography, the percentage stenosis of the lesions in Group 2 (39.7 +/- 16%) remained significantly lower than before angioplasty (p < 0.0001). Six of these lesions (19%) developed restenosis. In Group 1, the percentage stenosis at control (39.5 +/- 18%) was comparable to that before angioplasty. Moreover, 5 lesions in Group 1 (17%) which were initially non-significant had > 50% stenosis at the 6 month control. These results show that dilatation of non-significant coronary stenosis during multiple revascularisation procedures is not common and should be avoided. Not only is there no benefit at 6 month control angiography but also the procedure may accelerate the evolution of the atherosclerosis.