The variation of the electro-optic decay times with the intensity and frequency of the applied electric field are investigated for a colloid system of rigid rod-like particles. In the kilohertz frequency range the decay process is consistent with field-free Brownian disorientation and the time constants are sensitive to interparticle electrostatic interactions. The abrupt rise in the electro-optic relaxation times accompanied by a decrease in the saturation value of the effects, observed in the process of deionization of the medium, indicates a phase transition from a gas to a liquid-like state of the colloid system. At low frequencies (hertz range and de pulses) the decay times are reduced by an additional effect, most probably of a hydrodynamic nature.