This study was undertaken to evaluate the efficacy of a new technique of regional liver hyperthermia using the femoro-hepatic arterial (FA.HA) thermal bypass. With mongrel dogs (n = 5), an 8 F catheter was placed in the hepatic artery (HA) through the gastroduodenal artery. A 12 F catheter was introduced into the abdominal aorta through the right femoral artery (FA). These catheters were connected to a system containing a centrifugal pump and a heat exchanger. The heat exchanger consists of warmer coils and a water bath kept at a temperature of 47 degrees C. The bypass was run at an average blood flow rate of 160 +/- 20 (mean +/- SD) ml/min. The temperature was continuously monitored at four measuring points of water bath, inflow blood of HA, liver parenchyma and rectum. The temperature of liver parenchyma promptly reached 42.1 +/- 1.1 and 42.8 +/- 0.8 degrees C 20, 30 minutes after the start of hyperthermia, respectively. The rectal temperature remained 39.3 +/- 1.2 degrees C at 30 minutes. These results indicate that our method is simple and highly effective to perform regional liver hyperthermia.