Biaxial stress fatigue data is carefully examined in order to determine how much foundation exists for a rational approach to classical stress-based fatigue limit analysis involving biaxial stress components. A review is given of the methods presently in vogue, and new methods are suggested for obtaining equivalent mean and equivalent alternating stresses. Some groundwork is laid for the consideration of stress gradient influence on fatigue behavior. There are also some observations concerning the Distortional Energy and Tresca criteria and how they are incorporated in fatigue design procedures. The work is restricted to cases in which the alternating principal stress axes have fixed orientation. / Ph. D.