To elucidate changes in hormone metabolism, especially thyroid, cortisol and sex hormone metabolism, during acute local heat stress, serum-free thyroxine (FT4), free tri-iodothyronine (FT3), reverse T3 (rT3), thyroxine binding globulin (TBG) and a number of other hormone levels [thyroid-stimulating hormone, thyroglobulin, calcitonine, luteinizing hormone, follicle-stimulating hormone, prolactin, growth hormone, cortisol and testosterone] were measured sequentially in 11 male patients with bladder cancer during and after local radiothermotherapy treatment. Hyperthermia was administered using 8 MHz radiofrequency (RF) capacity equipment. The core temperature was raised from 37 to 42 degrees C and maintained at 42 degrees C for 1 h. No significant change in hormone levels except for a slight decrease in TBG levels was observed. The clinical results indicated that 8 MHz RF hyperthermia at 42 degrees C can be applied safely as a therapeutic measure in patients with bladder tumours. Further studies concerning the changes in TBG are necessary in patients with other tumours, especially those with the complication of subclinical hyperthyroidism, to detect any corresponding rises in FT3 and FT4 levels. The effects of using higher temperatures also need to be examined.