The existing models for the “classical” Portevin-Le-Chatelier effect have been analyzed, and the non-linear dynamical model has been proposed in order to quantify the nature of temporal instabilities in fatigued metallic alloys. The model employs the concept of a positive feed-back among the populations of mobile, immobile and Cottrell-type dislocations with atmospheres of point defects. Three major types of loading have been numerically simulated: pure sinusoidal, creep fatigue (“the Lorenzo-Laird bursts”) and ramp loading (“the Neumann bursts”, when the amplitude of otherwise cyclic loading grows linearly with time). Computer movies of the temporal evolution of stress and dislocation densities have been prepared as an aide for analysis and illustration. The model successfully reproduces stress serrations in terms of the underlying dislocation mechanisms and thus for the first time establishes a fundamental link between the micro-and macromechanics of cyclic deformation.