Acute occlusion and restenosis are the major complications of percutaneous transluminal coronary balloon angioplasty. Application of heat during balloon dilation was postulated to reduce these complications. We evaluated thrombogenicity and intimal hyperplasia of normal rabbit iliac arteries after conventional (37 °C) and thermal balloon dilation. Thermal dilation was performed with a radio-frequency-heated balloon, provided with three thermocouples attached to the inside of the balloon skin. In a previous in vitro study, thrombogenicity of human subendothelium was increased at 55°C and greatly decreased at temperatures over 70°C. Thermal balloon dilation was therefore performed at 55 and 90°C in vivo. Rabbits survived 2 h for evaluation of platelet adhesion or either 3 or 8 weeks for intimal hyperplasia. Angiograms revealed no occlusions or thrombi after any procedure. Platelet adhesion was quantified on 20 scanning electron microscopic pictures per balloon dilation site and was expressed as the percentage of the luminal surface covered by platelets. Platelet adhesion was similar in all groups, although large thrombi were present in the 90°C group. Intimal hyperplasia was measured morphometrically at regular intervals over the balloon site. After 3 weeks, the average intimal hyperplasia was significantly reduced in the 90°C balloon dilation group, which was mainly due to the absence of intimal hyperplasia in the mid-part of these segments. After 8 weeks, intimal hyperplasia was equal in all groups. Thus, in the applied model, platelet coverage was equal after conventional balloon angioplasty and after 55 and 90°C balloon angioplasty. Our data suggest that intimal hyperplasia is delayed but not diminished after balloon dilation at 90°C.