The hydrogen and nitrogen effects on fatigue life of austenitic steels are discussed using the ab initio calculations of electron structure, analysis of atomic distribution and dislocation substructure. As shown, both elements increase the concentration of free electrons in the f.c.c. iron softening thereby the crystal lattice, decreasing specific energy of dislocations and increasing their mobility. As a result, the dominant occurrence of short-range atomic order in the metal solid solutions causes localization of plastic deformation and consequent formation of dislocation slip bands. A combination of these factors realizes in the localized reversible planar slip of dislocations, which prevents their intersection with nucleation of submicrocracks and decreases the crack growth rate during fatigue tests, i.e., prolongs the fatigue life.