The crystal fields of CeCl₃, PrCl₃ and NdCl₃ are investigated through electron spin resonance measurements on gadolinium ions introduced as impurities into these crystals. The crystal field parameters of the appropriate spin Hamiltonian were derived for all three crystals. Because the crystals all have paramagnetic host cations, the electron spin resonance lines were very broad and overlapped extensively. A study was made of possible mechanisms giving rise to such line widths and it is concluded that a motionally narrowed dipolar broadening mechanism can fairly satisfactorily account for the observed linewidths.