Antitumor effects of pre-transplantation hyperthermia and its correlation to immunological changes in the host animals and enhancement by dietary unsaturated fat have been studied. Leg muscles of mice were locally heated (41 degrees-43 degrees C, 40 min) and fibrosarcoma cells were inoculated into the heated and unheated sites and tumor growth time was determined. Spleen cell activity and plasma levels of interleukins (IL1 and 2) [RIA kits] were assessed. Muscle and tumor fatty acid profiles were modified by feeding mice with unsaturated fat supplemented diet and analysed by GLC. Pre-transplantation hyperthermia suppressed the tumor growth on both heated and unheated contralateral legs of mice. These effects were associated with increased spleen cell activity and plasma levels of IL1 and 2. Diet rich in unsaturated fat altered the fatty acid profiles of the leg muscles and tumors and inhibited tumor growth. It also potentiated the antitumor effect of pre-transplantation hyperthermia. In conclusion, mild local hyperthermia induces both direct and abscopal antitumor effects which may be ascribed to stimulation of host's antitumor immune responses and these effects are augmented by unsaturated fat supplemented diet.