This paper presents an interface relaxation finite element-boundary element coupling method (FEM-BEM coupling) for elasto-plastic analysis. The method is capable of handling problems with natural boundary conditions (BC) applied at the entire real boundary of the FEM or BEM sub-domains. That specified BC set could not be imposed using existing domain decomposition coupling algorithms. In the paper we present applications dealing with elasto-plastic analysis in infinite domains. The calculation results obtained by means of the presented method are compared with those by conventional finite element models and, if available, analytic solution.