An instrument consisting of a copper vapor laser coupled to an optical fiber/chemical injector catheter for the treatment of occluded arteries has been constructed and tested. The combined application of three steps: the pre-irradiation injection of a light absorbing dye, HPD; brief copper laser irradiation (at 578 nm); and a urokinase infusion after the irradiation, produced the striking effect of liquefaction and resolution of thrombus. The histological examination of the arteries after the treatment showed no apparent damage to the arterial wall.