Whole body hyperthermia was induced in older, tumour-bearing dogs using a radiant heat device. Dogs were anaesthetized (thiopental), paralysed (atracurium), and mechanically ventilated (100 per cent O2) during the heating procedure. Heart rate, systolic/diastolic, and mean arterial blood pressure, and arterial blood gases were monitored throughout the procedure. Serum biochemical parameters, complete blood count, and coagulation profiles were evaluated before, during, and after whole body hyperthermia. Significant increases (p less than 0.05) were noted in heart rate, systolic pressure, diastolic pressure, and mean arterial pressure during the treatment period. A significant decrease in arterial oxygen partial pressure due to unknown causes occurred during the treatment period. Clinical evidence of cardiac decompensation was not manifested in any dog following whole body hyperthermia. Total white blood cell count, neutrophil count, alkaline phosphatase, and creatinine kinase were significantly (p less than 0.05) increased 24 h following whole body hyperthermia. These elevations returned to normal within 1 week of treatment in all dogs. Changes in coagulation profiles 24 h following the procedure were not clinically significant. Adequate pretreatment evaluation of cardiovascular, metabolic, and haemostatic function in tumour-bearing dogs is necessary to identify candidates for treatment with systemic hyperthermia. Otherwise healthy, tumour-bearing dogs withstand the physiological stress of whole body hyperthermia without significant acute or persistent toxicity and represent a valuable model for whole body hyperthermia research.