  Single pion production off nucleons is studied in the framework of
relativistic baryon chiral perturbation theory at tree level with the inclusion
of the terms from the dimension two effective pion-nucleon Lagrangian. The five
appearing low-energy constants are fixed from pion-nucleon scattering data.
Despite the simplicity of the approach, most of the existing data for total and
differential cross sections as well as for the angular correlation functions
for incoming pion kinetic energies up to 400 MeV can be satisfactorily
described.
