Worldwide clinical Experience with Percutaneous Coronary Angioscopy using the Baxter ImageCathTM system has exceeded 3000 procedures since first introduced in July 1991. In spite of extensive investigation into a broad range of applications, a proven clinical indication has yet to be defined, thus restraining the technology from general clinical use. Although coronary angioscopy has provided unique insight into coronary artery disease, the inherent qualitative nature of angioscopic data has limited the scope and breadth of the findings. Indeed, a study of experienced investigators has shown that consistent inter-observer agreement is limited to the presence of thrombus or dissection. Various methods of image quantification attempt to overcome the limitations inherent in angioscopic data. Current research in the areas of direct lumenal measurement, computerized color analysis, and spectroscopy promise to provide reliable image interpretation and possible correlation of image content to clinical syndrome.