The development of efficient thermoelectric semiconductors such aspandntype bismuth telluride has given rise to a variety of applications of thermoelectric cooling in the field of instrumentation.3,4This paper is concerned with the application of thermoelectric cooling to a load in which the heat produced, by the microwave power absorbed, is balanced by the heat extracted thermoelectrically. By this means the load may be maintained at the temperature of its surroundings, in which case extraneous heat transfer is reduced to zero. A restriction is applied to the temperature drop across the thermoelements used, and it is shown that the cooling power required to balance the microwave power may then be evaluated from the Peltier coefficient and two values of direct current.A simple form of waveguide termination is described to which distributed cooling is applied. It is concluded that the type of waveguide load required, to approach the inherent accuracy of the method, will be closely approached as the wavelength decreases into the millimetre band.