Abstract: A system for generating heat and sensing the temperature in an internal body organ such as in a tumor and for gaining information about the tumor for diagnosis and other purposes comprising a first system portion which is preferably entirely implantable beneath the skin of the person being treated or diagnosed including a probe device having electrical heater and sensor elements in it for implanting extending into the tumor to be treated and including an internal control unit also implantable under the skin and operatively connected to the heater and sensor elements in the probe, the internal control unit also including an electronic control unit for controlling the energizing of the heater element and having a sensor responsive portion responsive to the temperature sensed by the sensor element, and a transmitter/receiver device and a second system portion including an external control unit having a transmitter/receiver device for positioning on the skin adjacent to the internal transmitter/receiver device fo