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The exposure of normal mice to whole body hyperthermia (1h WBH at 39 or 40°C), 20 or 48h prior to total body irradiation (TBI) with lethal doses of γ-rays affords significant protection as assessed by survival. The radioprotective effect of WBH, as observed in normal mice, diminished in tumour bearing mice depending upon the size of tumour. Treatment of tumour bearing mice with mild WBH, 20h prior to local irrradiation (LIR), did not protect the transplanted tumour against radiotherapy with a single dose of 20Gy or fractionated dose (in five fractions) of 7.5Gy on alternate days. In fact, mild WBH treatment enhanced the tumour regression and increased the mean survival time after fractionated dose therapy. However, the prior mild WBH was found to be ineffective in protecting normal tissue, as assessed by skin contraction after local irradiation (50Gy). This indicates that mild WBH treatment given 20 h prior to local radiotherapy enhances fibrosarcoma tumour regression but cannot protect skin (normal tissue) against local irradiation. It appears that radioprotection of animals by WBH may be the consequence of its radioprotective effect on haemopoietic tissues mediated through certain cytokines. Perhaps WBH may not have a radioprotective effect on other tissues, as evident from skin contraction studies. [ABSTRACT FROM AUTHOR]