Studies of the properties of the radiation occurring in channeling of relativistic electrons and positrons, carried out over the last eight years, have shown that it is possible to study a number of properties of single crystals on the basis of the features of the radiation spectrum and the location and width of the spectral lines. The greatest success in this area has been achieved in determination of the Debye temperature of crystals, more accurate determination of the crystal potential, and determination of the density of electrons near crystal strings and planes. As a consequence of the localization of relativistic electrons or positrons near certain atomic planes or strings, the radiation spectrum of the channeled particles, in contrast to diffraction methods, carries direct information on the crystal potential. The method permits study of the correlation of thermal vibrations of the atoms in the lattice, and also of some features of superstructures and complex crystals.