A flash method for the measurement of the thermal diffusivity of metals up to 1800°C is described. A high intensity short duration light pulse is absorbed in the front surface of a thermally insulated specimen a few millimeters thick heated in an induction furnace and the resultant temperature history of the rear surface is measured by a lead sulfide cell, displayed on an oscilloscope, and photographed by a Polaroid Land camera. The thermal diffusivity of the material is determined from this temperature versus time curve provided the theoretical boundary conditions are experimentally satisfied. Measurements of the thermal diffusivity of Armco iron, molybdenum, and titanium have been made.