A new development in temperature control is presented. This consists in using a Wheatstone beridge in a proportional thermostat both as a monitoring and a heating unit. The sensor is a copper wire closely and evenly wound around the volume to be temperature controlled. The other bridge resistors are manganic wires and are wound around the same volume. The theoretical limit of control is l part in ten billion of the sensor resistance. In practice the stability of the resistors and the design of the thermal system limited somewhat the temperature stability. Tests at 25 and 37 degrees C operating temperatures showed a term drift, including the drift of the relatively modest system used to measure the temperature.