A minicomputer-based system was designed to control the microwave (2.45-GHz) power to four local hyperthermia applicators. Errors in temperature measurement, due to electromagnetic field interactions with small thermocouple probes, are minimized by sampling the temperature only when the microwave power is off. The programmable controller can regulate the temperature in tumors in 0.1 degree C increments from 30 to 60 degrees C. This technique reduces temperature differences throughout the tumor at steady state to less than 0.4 degrees C and prevents skin burns.