[en] Formulae for spin susceptibility, ESR line width and shift of resonance frequency of paramagnetic ions in a state with variable valency are derived. Agreement between temperature dependences of theoretic and experimental parameters of ESR spectra of nonsuperconducting YBa₂Cu₃O₇ ceramic phases is ascertained. An assumption is made thta with the growth of oxygen index in YBa₂Cu₃O_x from 6.1, copper ion valency drops in Cu1 position and for superconducting phases of this ceramic it acquires < or approx 1.6-1.7 values. This fact explains as well an abrupt drop of ESR signal intensity in superconducting YBa₂Cu₃O_x samples