[en] The authors analyze the epithermal and thermal portions of the energy spectrum of neutrons in the lattices of water-cooled, water-moderated power reactors based on experimentally determined spectral indices of eight isotopes. The obtained values of the thermal spectral indices are compared with those calculated by the programs YAM(A) (Monte Carlo method), THERMOS, and the variant program POP. The data obtained with the first two programs agree fairly well and are in line with the experimental data; the POP program predicts excessively rigid spectra. It has been established experimentally that the neutron flux in the epithermal region falls away more slowly than the 1/E-dependence