  We present a study of the magnetic properties of YNiO$_{3}$ in the
paramagnetic range, above and below the metal-insulator (MI) transition. The dc
susceptibility, $\chi_{dc}$ (measured up to 1000 K) is a decreasing function of
T for $T >$150 K (the N\'{e}el temperature) and we observe two different
Curie-Weiss regimes corresponding to the metallic and insulator phases. In the
metallic phase, this behaviour seems to be associated with the small ionic
radius of Y% $^{3+}$. The value of the Curie constant for T$<$ T$_{MI}$ allows
us to discard the possibility of Ni$^{3+}$ localization. An electron spin
resonance (ESR) spectrum is visible in the insulator phase and only a fraction
of the Ni ions contributes to this resonance. We explain the ESR and $\chi
_{dc}$ behaviour for T $<$ T$_{MI}$ in terms of charge disproportionation of
the type 2Ni$% ^{3+}\to $ Ni$^{2+}$+Ni$^{4+},$ that is compatible with the
previously observed structural transition across T$_{MI}$.
