A dual-laser system (helium-cadmium and pulsed dye) capable of continuous computer analysis of spectroscopic characteristics of tissue fluorescence, which can distinguish atherosclerotic plaque from components of normal arterial wall, was used to deliver laser energy to ablate plaque. During a 1-year period this system was used to facilitate balloon angioplasty of short (3 to 17 cm) total occlusions of the superficial femoral or popliteal arteries only when standard angioplasty techniques were ineffective. During the year of the study, in one institution 415 patients were subjected to arteriography of the lower extremities for leg ischemia (397 for limb salvage indications). Standard angioplasty techniques were used in 94 of these patients; 218 patients were unsuitable for standard angioplasty, did not fulfill criteria for "smart" laser treatment, and underwent standard bypass operations. Only 11 patients (plus six others in the second institution) requiring treatment fulfilled the criteria for use of the "smart" laser. In 10 patients the occluding lesion was traversed by the laser wire (diameter 0.021 inch), and luminal patency was effectively restored by balloon angioplasty to greater than or equal to 70% of the most normal-appearing segment of that artery. Satisfactory luminal patency has persisted for 2 to 12 months (mean 6 months) in nine patients; the lesion in the tenth patient restenosed at 3 months. The laser procedure was unsuccessful in all three patients with occlusions greater than 10 cm and in four others. Although there were three microperforations with the laser wire, there were no clinically significant complications.(ABSTRACT TRUNCATED AT 250 WORDS)