This paper describes a computer controlled testing system that is capable of performing complex thermomechanical fatigue tests. Three different tests have been developed: 1. High temperature compression (HTC) tests in which the gage length of the specimen is held at constant length and the mechanical strain is totally imposed by the triangular temperature cycle. 2. High temperature tension (HTT) tests in which the mechanically imposed length change is exactly double the thermally induced length change. 3. Multiple isothermal deformation (MID) tests for which the deformations occur isothermally and the temperature is changed every half cycle while maintaining constant mechanical strain.