Direct visual examination of the interior surfaces of intact human coronary arteries is now a reality, both from intraoperative and transluminal approaches. As an additional investigation to angiography it improves the knowledge about the corresponding morphology of angiographically visible changes. Since the first report about percutaneous and intraoperative coronary angioscopy by Spears et al. in 1982 important indications concerning the intraoperative approach were defined such as the control of coronary atherectomy, intraoperative balloon dilatation and laser angioplasty, the inspection of the grafts prior to implantation and the assessment of the quality of the distal anastomosis after graft insertion. The most important clinical result angioscopy has brought about is the postulation of a concept of the different clinical forms of coronary artery disease based on the morphological stages of atherosclerosis, which were defined by angioscopy and could be related to clinical symptoms. Scientific studies today are concerned with determinants for the patency rate of bypasses, the restenosis rate of PTCA, the acute and chronic effects of drugs, and the mechanism of all kinds of catheter-supported angioplasties. The next important application of coronary angioscopy will undoubtedly be the simultaneous visual control of coronary angioplasty procedures such as laser angioplasty and other new methods.