In order to study the morphologic changes after CO2 laser irradiation, 42 rat femoral arteries were irradiated under various conditions at different time intervals from zero to three weeks. The arteries were examined under transmission electron microscope (T.E.M.), and 30 mW power and 0.3 to 0.5 mm/sec velocity were considered to be the most suitable for a CO2 anastomosis of small femoral arteries.