Basic studies were carried out on the treatment, with argon laser and balloon dilatation catheter, of stenotic arteries resulting from atherosclerotic plaque. Seventeen rabbits approximately 34 weeks old and weighing between 3 and 4 Kg were used. Each rabbit was fed a 1% cholesterol diet for 3 to 4 months to induce atherosclerotic lesions in the carotid arteries and the aorta. The argon laser unit used was a Model 20 Endocoagulator (HMG, Inc.; maximum power, 12W). Under an angioscope, two bare-ended laser probes (1.5 mm and 0.3 mm in diameter) were used to vaporize atheromatous plaque in the aortas of 10 rabbits, and a metal tip laser probe in the case of seven rabbits. The plaque remaining after this laser angioplasty was compressed to the luminal surface through inflation of a balloon catheter (balloon angioplasty) in order to sufficiently dilate the arteries. The animals were then sacrificed and examined both macroscopically and microscopically. When the bare-ended probes were used, there was a change in the depth of vaporization in line with the direction of the laser beam. Using a laser heating power of 25 J, perforation of the vessel wall was observed in 36% of the trials. A higher frequency of perforation was seen with the 0.3 mm probe than with the 1.5 mm probe. However, a constant vaporizing effect was achieved using the metal tip laser.(ABSTRACT TRUNCATED AT 250 WORDS)