To investigate the effect of radiofrequency energy (600 kHz) on atherosclerotic tissue, high frequency current was applied on 160 specimens of human abdominal and iliac artery autopsies with various duration and energy density. All experiments were performed in air, saline, and blood. Application of 5 to 30 joule resulted in coagulation of the intima and the media. Time dependent a shrinking of the vessel wall did occur at energy rates above 30 joule. At higher energies vaporization was found. In blood coagulation at the catheter tip became evident at 30 joule and higher energies. Histologic cross sections showed distending of intimal layers at 25 joule, additional shrinking of medial layers at 50 joule, vacuoles at 75 joule and separation of intima layers from underlying layers at 200 joule. In vitro application of high frequency current on atherosclerotic tissue results in thermal effects only. The extent of these effects seems to be unpredictable because of the ever changing composition of the tissue, resulting in changes of energy delivery at the tip tissue interface. On calcified plaques an energy dependent contraction mainly of adjacent vessel wall could be seen. Because of the non-predictable effects and adverse side effects on adjacent normal vessel wall the method seems not to be useful for clinical application.