It is important to reduce a systemic stress during regional hyperthermia against upper abdominal malignancies. A 50 mg indomethacin suppository was administered to five patients with intrahepatic tumour 30 min before hyperthermia. Oral temperature only rose to 37.8 degrees C, heart rate increased to just 110/min, and systolic blood pressure only increased to 134 mmHg. Under these conditions, epinephrine and norepinephrine rose to only 0.09 and 0.25 ng/ml, respectively, which were within normal limits. In addition, prostaglandin E2 (PGE2) did not increase at all. However, when these same five patients were not pretreated with indomethacin, parameters monitoring the systemic condition rose profoundly during hyperthermia. Systemic stress during hyperthermia against upper abdominal malignancies was reduced by the indomethacin pretreatment.