Recent developments in optical instrumentation have made possible the direct, three-dimensional viewing of intravascular structures. Using an angioscope (the Trimedyne Optiscope, Trimedyne Inc., Santa Ana CA) and a xenon cold lamp (the Xenon Cold Light Fountain, Karl Storz Endoscopy America, Inc., Culver City, CA), the authors have visualized, without complications, the normal orifices of various arteries and their bifurcations in 12 dogs, the atherosclerotic aortas of eight post mortem humans, and the coronary arteries of six post mortem humans. Potential applications of the instruments include more accurate diagnosis of occlusive diseases of the blood vessels, evaluation of such interventional procedures as angioplasty, intraoperative assessment of anastomoses, and safer laser surgery. The angioscope also enables the physician to combine pressure recording and dye injection simultaneously with the visualization of the inner walls of the vessels.