The previously reported work on the spherical harmonics treatment of epithermal-neutron spectra in reactor lattices is further extended and improved. The condensed matrix representation is introduced for the space- and lethargy-dependent vector of the spherical harmonics flux moments. Detailed recurrence relations for the factors resulting from numerical integration of the lethargy transfer integrals, in both the fast and the resonance regions, are provided. For solving systems of interface and boundary condition equations in the space variable, a procedure based on the coefficient matrix partitioning is presented.