We have performed an isospin analysis of single-pion production processes in antiproton-nucleon scattering from threshold to 2.90 GeV/c. Reactions used are pp→ppπ0, npπ- and pp→ppπ-. Results show that σ1, the total I=1 cross section, rises rapidly from threshold to reach a broad maximum around 2.5 GeV/c and σ0, the I=0 cross section, rises from threshold and continues on a linearly rising trend at least up to 2.90 GeV/c. In the region of 2.9 GeV/c, σ1 and σ0 have comparable values, thus suggesting that considerable amount of I= 1 2 Nπ and Nπ states is produced even in this low momentum region. We further determine that single pion production processes are not the source of the π0 (2375,190) enhancement observed in the pp and pd total cross sections and may account for as much as 25±8% of the π1 (2350,140) enhancement. © 1974.