Discontinuities of microstructure in steels induce stress concentrations. Microplasticity is the plasticity which exists locally at these stress concentrations, whereas the remainder of the material is in the elastic domain. The microplasticity threshold is the nominal stress in uniaxial loading from which microplasticity exists. During fatigue tests, this threshold has been determined for the 304 L stainless steel by measurements of temperature variations, informations derived from hysteresis loops, observations of microstructure at the surface of polished specimens. The microplasticity threshold of the studied material is between 60 and 75 MPa.