Effects of laser radiation on atherosclerotic plaques were evaluated in vitro and in vivo. Necropsy artherosclerotic femoral and coronary arteries were submitted to a laser beam. Arteries were perfused by saline or blood solution and a silicone fibro-optic system was placed near the plaques through a balloon dilatation catheter. After laser radiation (20 to 40 W, 2 to 10 seconds) angiograms and histologic sections were obtained. Aorta of 20 atherosclerotic New Zealand rabbits was exposed in dry condition to a CO2 laser beam (2-4 W, 0,2 second). After reinstatement of blood flow, animals were sacrificed from 24 hours to 3 weeks for microscopical examination. In vitro studies showed a significant recanalisation of the thrombosed arteries under blood flow but not under saline solution. Histologically the laser radiation produced a crater surrounded by thermal intimal damage and decollated calcified plaques. In vivo studies showed the healing process: no perforation, no aneurysm, no thrombosis occurred. After 24 hours the crater was filled with a non extensive thrombus, on the first week the thrombus contained phagocyte cells and on the third week, the endothelial damage was completely healed. These results suggest that laser radiation may be effective to recanalize totally occluded arteries in human.