The effects of a metal probe catheter on tissue using radiofrequency (RF) as its energy source is evaluated. The energy dissipation and the temperature increase of this probe was compared with a laser-heated probe. After 15 seconds, the temperature rise of the RF-heated probe at a maximum power setting was 68°C in water and 106°C in plasma. In contrast, the temperature rise of the Nd: YAG laser-heated probe after 10 seconds, 10 watt(W), was 80°C in water and 595°C in plasma. Calorimetric experiments showed that in a 7 to 30 W range of the power setting for the RF generator, only 3.5 to 4.5 W was dissipated at the RF catheter tip. Using axial forces equivalent to 100 g in fatty tissue, the penetration velocity of the RF-heated probe was 0.015 mm/s, with a temperature rise of the tip of 180°C; whereas the velocity of the laser-heated probe was 3.4 mm/s with a temperature rise of the tip of 300°C. These in vitro results suggest that during clinical application, tissue in contact with the front surface of the RF-heated angioplasty probe will be remodeled, whereas with the laser-heated probe tissue will be vaporized circumferentially. The RF-heated probe's risk of vessel wall perforation is probably small.