Seventy-six patients with complete occlusion of the iliac, femoropopliteal or distal arteries underwent laser angioplasty after failure of attempted mechanical recanalization by conventional angioplasty. The energy source was a dye pulsed laser emitting at 480 nm, 2 microseconds, 35 to 50 mJ/pulse and 5 Hz. The laser was coupled with an optical fiber of 200 microns diameter covered by a metallic spring. In order to center the laser in the arterial lumen, the fibre optic was introduced with a balloon catheter or a modified Van Andel catheter with a tapered and curved distal end with controlled torsion to direct the laser towards the lesion to be treated. The therapeutic laser was connected to a diagnostic Helium-Cadmium laser emitting at 325 nm, 50 ms and 5 mW, for the induction of tissue fluorescence analysed by a multichannel detector, itself connected to a computer programmed to differentiate atheromatous from normal tissues. The therapeutic laser was only activated when atheromatous tissue was in contact with the distal tip of the fiber optic. After vaporizing a narrow pilot channel conventional balloon angioplasty was performed. The immediate success rate was 83%; it was higher in iliac than in femoral arteries. This was less dependent on the length of occlusion than on the presence of calcification which was a common cause of failure. The complications were immediate reocclusion, perforation due to the sharp tip of the fibre and dissections without major clinical consequences. After 18 months, 64% of the arteries remained patent.(ABSTRACT TRUNCATED AT 250 WORDS)