  We calculate isospin breaking in pion-nucleon scattering in the threshold
region in the framework of covariant baryon chiral perturbation theory. All
effects due to quark mass differences as well as real and virtual photons are
consistently included. As an application, we discuss the energy dependence of
the triangle relation that connects elastic scattering on the proton pi+- p -->
pi+- p with the charge exchange reaction pi- p --> pi0 n.
