The behavior of GaAs crystals irradiated with neutrons of various fluence has been investigated using Rutherford backscattering spectrometry/channeling. The results show that the neutron irradiation (from 10(14) to 10(17) n/cm(2)) has little effect on the critical angle (Psi(1/2)). During annealing, the rate of lattice reordering increases with the temperature rising. For the fluence of 10(15) n/cm2, the activation energy of defect annihilation E-1 = 0.35 eV, which may be attributed to the recombination of vacancies with migrating interstitials. The activation energy E-2 = 0.13 eV for the neutron fluence of 10(17) n/cm(2) may. probably, correspond to the recombination of vacancies with interstitials in the most neighborhoods.