Abstract: A thermoregulated magnetic susceptibility sensor assembly for well-logging or the like is disclosed. The assembly includes a sensing solenoid and a non-metallic container for the sensing solenoid. Located in the container and spaced from the sensing solenoid are a plurality of heaters. These heaters are uniformly positioned about the sensing solenoid and a heat transfer material is located between the heaters and the sensing solenoid. The heat transfer material conducts the heat from the heaters to the sensing solenoid in a substantially uniform manner so that the sensing solenoid is maintained at a uniform temperature. Preferably, temperature sensors are provided to control the heat output of the heaters to maintain the sensing solenoid at the desired uniform temperature. To minimize heat transfer to the heaters from the external environment, a layer of insulation is provided around the heaters.