Hyperthermia for treatment of cancer is known to be beneficial both in itself and in conjunction with other forms of treatment, particularly radiotherapy. We have developed a new machine for local hyperthermia (41-44-degrees-C) to the prostate, by transmission of microwaves (915 MHz) via a rectal probe. Patients were treated on an outpatient basis and did not require any anesthesia or sedation. There were no complications. Good results, measured by local control, disappearance of malignancy, relief of obstructive symptoms and pain, have been obtained in a series of 44 cases. More studies with this promising new modality are in progress.