The characteristics of two modified fiber tips, the metal laser probe and the rounded sapphire contact probe, were examined in vitro and in vivo with respect to some of the risks of laser angioplasty. Both probes have an atraumatic, blunt shape. The laser beam profile of the sapphire contact probe looses its focussing properties in water. In vitro, we found a large temperature gradient from the front to the rim of the probe. Ablative temperatures were reached at the tip whereas the temperature of the metal connector near the rim of the sapphire crystal rose only 30 °C in blood when 15 W Nd-YAG was applied for 1 s. In contrast, the metal laser probe reached temperatures over 500 °C in an in vitro tissue/blood environment when 10 W was applied for 5 s. The metal probe ablated both in the forward and the radial direction. In a rabbit model there was a large variation in temperature of the metal in vivo (70 - 320 °C). The highest temperatures were associated with acute complications. However, in spite of transmural coagulation necrosis the artery wall remained functionally intact during a follow up period of up to 56 days.