A PET-controiled multithermocouple system employing Analog Devices 4 channel amplifiers has been constructed. The intended application of the equipment is the measurement of the temperature distribution in patients receiving microwave hyperthermia as part of cancer therapy. The equipment has been shown to be sufficiently accurate and, in addition, is not susceptible to r.f. interference at the power levels in use in this hospital for microwave hyperthermia.