Preoperative and postoperative angiograms were compared in 81 patients who had undergone coronary artery bypass surgery. In these patients, 135 bypassed vessels had had critical stenoses or total occlusion; 99 of these bypasses (73.3%) were patent. Of 36 bypassed vessels that had had noncritical stenoses, 26 (72.2%) were patent. This difference was not significant. Thus, competitive inflow does not lead to excessive graft failure in noncritically diseased vessels, and they can be bypassed with the same expectation of success as critically obstructed vessels. The risk and the advantages of bypassing mild lesions at the same time that severe obstructions are surgically treated are discussed.