Hyperthermia - the sustained controlled heating of tissues to 42-44 °C - is studied and used as a means of treatment in particular to destroy malignant cells selectively. This may be achieved by heat alone, or in conjunction with other forms of treatment, such as radiotherapy or chemotherapy, thanks to the synergistic effect obtained. A new microwave apparatus has been designed and developed which enables precise, controlled and safe hyperthermic treatment of the human prostate. Following extensive laboratory and experimental studies, a first treatment series on humans has been carried out. The initial observations on our first 192 treatments in 32 patients is reported here.