The object of this study was to determine whether transverse radiotomography, despite cardiac movement, could be used to visualise aortocoronary bypass grafts to confirm their patency or obstruction. The results were then compared with those of coronary angiography. 20 patients with a total of 38 grafts (18 on the left anterior descending, 8 on the circumflex and 12 on the right coronary artery) underwent tomography. 1 or 2 60 ml boluses of iodide contrast medium were injected into a fore arm vein and 3-5 films were exposed after each injection at 15 sec intervals. Coronary angiography was performed in 16 patients and the results of tomography were identical to those of coronary angiography : 23 patent and 6 occluded grafts. In one case, subtotal proximal stenosis of the left anterior descending artery allowed sufficient flow for the graft to be opacified and considered patent on tomography. The correlation between transverse radiotomography and coronary angiography was excellent. Transverse radiotomography, a non-invasive technique, is very useful in operated patients with atypical chest pain and in those with recurrent angina in whom obstruction of the graft is feared. It does not seem destined to replace control coronary angiography after bypass surgery, but it may be indicated is selected cases.