In this paper authors propose an energy fatigue hypothesis. Simulations results of material behavior in a fatigue process will be presented. Simulations were programmed in Matlab environment with the assumption of an elastic-plastic material model and fatigue changes according to the energy hypothesis. Constant amplitude, symmetrical load cycles as well as programmed were taken into an account. Encountered problems and their solutions will be discussed also. Model parameters identification for the relation between stress, strain and energy responsible for fatigue changes was conducted on the basis of an experimental data for constant amplitude loads. A road map leading to programming simulation of multiaxial models for symmetrical pseudostochastic loads will be described.