Abstract: A thermal cycling apparatus having an upper heat chamber and a lower cold chamber positioned vertically beneath the upper heat chamber and vertically coaxial therewith whereby a material to the thermal cycle tested can be transferred between the upper heat chamber and the lower cold chamber. An externally operated flapper door within the thermal cycling apparatus separates the two chambers. The material to be thermally tested is placed in a basket constructed of suitable material which can be translated between the two chambers from a location externally of the chambers. The temperature in the upper chamber is elevated by gaseous nitrogen to a temperature up to about 1000 degrees F. and the lower cold chamber is cooled by a cryogenic liquid. Cycle testing is preformed by alternately transferring the material, i.e. 40 or more specimens at a time, between the upper and lower chambers the number of times desired.