A method has been developed for taking thermal diffusivity data at elevated temperatures with a cylindrically symmetric sample consisting of a stack of disks. An axial heater is turned on and the temperatures at three radii in the midplane are recorded as functions of time. The temperature data from the inner and outer radii are used as empirical boundary conditions, and the temperature data from the middle radius are used to obtain the thermal diffusivity. A computer has been programmed to make the calculations by the method of finite differences. Thermal diffusivity measurements have been made from 26° to 895°C on Armco iron. The values found for the thermal diffusivity by this radial method agree well with the values found by Shankset al.who used a longitudinal method with a finite rod. The radial method is particularly advantageous when samples in the form of disks, but not in the form of long rods, are available.