Isospin violation in the two-nucleon system

In this contribution violation of isospin symmetry of the nuclear forces is investigated using the effective field theory of the Standard Model, Chira l Perturbation Theory (chi PT). Without going into details of the underlyin g Nuclear chi PT, we concentrate on the construction of a systematic expans ion of isospin breaking effects (electromagnetic interaction and quark mass difference) at the level of a chiral Lagrangian. First results especially for the S-1(0) threshold paramters are shown.