The following studies were performed to develop a new technique of hyperthermia by vascular catheterization for the treatment of malignant neoplasm. A balloon catheter was inserted into the artery of a cancer-affected organ and inflation of the balloon temporarily occluded the artery, after which an anticancer drug solution warmed to 45 degrees C was infused. The purpose of this technique was to enable the solution to arrive at the affected area undiluted by blood. It would then remain in the organ and act on the lesion. When OK-432 was intravenously administered to induce pyrexia of 40 degrees C, followed by the above-mentioned arterial infusion, it was expected that the effects of hyperthermia and chemotherapy would be synergistic. In cases of liver cancer and urinary bladder cancer subjected to the arterial infusion of warmed anticancer drugs, however, the temperature in the hepatic vein increased by only 0.5 degree C while that in urethra near the tumor increased by only 1 degree C. In the future, further improvement needs to be made to obtain effective local heating with this technique.