The validity of the relationship between stress and strain-concentration factors proposed by Neuber, i.e., the geometric mean of the stress and strain-concentration factors is equal to the linear elastic-stress-concentration factor, is investigated for plane-stress problems. The physically nonlinear plane-stress problem of an infinite plate with a circular hole is solved by a perturbation method. Applicability of the solution and the restrictions on the relationship are discussed with reference to theoretical and experimental results.