This paper describes the working principles and operation of a new instrument for making absolute measurements of heat flow. This instrument, called the guarded cold plate apparatus, differs from standard guarded hot plate designs in that the measured heat flow through the sample is towards the metering side, rather than away from it. A guarded cold plate apparatus is described for measurement of the radiative heat flow from high emittance surfaces at temperatures up to 200 degrees C. Values of emittance obtained from such measurements agree with those derived from infrared reflectance data to within +/-5%.