[en] The pion production pn → ppπ^- and pp → ppπ⁰ are discussed. The theoretical analysis has been performed by using the models of heavy-meson exchange and pion-rescattering including the effect of nucleon resonances. The experimental data of the π^- production support the relative sign between the s-wave and p-wave pion-production amplitudes which is given by both of the two models. The d-wave pion production amplitude is discussed about the angular distribution of π⁰ production. The spin correlation observables give information about the partial wave amplitudes