The analytic solution is obtained describing kinetic equilibrium of the β-processes in the nucleonic plasma with relativistic pairs. The nucleons (n, p) are supposed to be non-relativistic and non-degenerate, while the electrons and positrons are ultra-relativistic due to high temperature (T > 6·10 9 K), or high density (ρ > µ10 6 g/cm 3 ), or both, where µ is a number of nucleons per one electron. The consideration is simplified because of the analytic connection of the density with the electron chemical potential in the ultra-relativistic plasma, and Gauss representation of Fermi functions. Electron chemical potential and number of nucleons per one initial electron are calculated as functions of ρ and T .