A system is described for delivering transurethral hyperthermia to the prostate. The system used a helical coil antennae powered by a 434 MHz generator. The antennae was housed in a disposable 22 Ch Foley catheter with water passed down the centre of the winding of the antennae and returned between the antennae and inner wall of the catheter. The flow rate of the circulating water could be varied. The position of the antennae was adjustable with respect to the balloon, essentially altering the length of the antennae. Urethral wall temperature was measured with a thermocouple passed down a small tube moulded into the outer wall of the catheter. Rectal temperature was measured using thermocouples placed in grooves machined into a custom made perspex rectal applicator. A computer program displayed the temperature and controlled the power to the generator. The SAR around the catheter was measured in a polyacrylamide gel phantom. However this does not take into account the effects blood flow and thermal conduction which may have important clinical implications. In order to investigate the actual temperature within the prostate during treatment, a group of patients underwent intraprostatic thermometry.