The effect of whole-body hyperthermia (41.5 degrees C, 2 h) on doxorubicin (DOX) tissue distribution and plasma pharmacokinetics was examined in rats bearing a subcutaneous fibrosarcoma. Tumour response to the hyperthermia regimen alone was minimal, but the combination of heat with DOX (5.0 mg/kg, i.v.) enhanced tumour growth delay. The combined therapy, however, showed increased toxicity to normal tissue (especially renal and cardiac). Although DOX levels in spleen tissue were higher in rats exposed to hyperthermia than in control normothermic rats, both groups had comparable levels of drug in tumour, heart, kidney, and small intestine tissue at all time-points examined. Compared with normothermic animals, hyperthermia-treated rats showed decreased DOX in the mean area under the concentration-time curve (AUC) and decreased plasma DOX t1/2 but increased plasma drug clearance. These heat-mediated alterations in DOX pharmacokinetic parameters, however, do not account for the significant increases in thermochemotherapy-mediated cytotoxicities observed in tumour, and in normal renal and cardiac tissues.