A materials testing system has been developed for isothermal and differential thermal fatigue testing of metal specimens. A closed-loop thermal cycle is provided by an induction heater and a gas-liquid cooling manifold. Mechanical control of the specimen, as a direct function of temperature, is provided by a closed-loop electrohydraulic system capable of operating in load, stroke, or strain control. A mechanical diametral extensometer was developed to work with soft materials. A unique specimen design and its related hardware make possible the investigation of materials of widely varying properties, including copper alloys and alloy steels.