Administration of sodium nitrite (an NO-generating preparation) doses of 11 mg/kg to rabbits was followed by motor disinhibition, with increases in myogram amplitudes in responses to nonreinforced flashes presented on a background of continuous illumination which served as a conditioned inhibitory stimulus; these changes appeared 1-1.5 h after administration and lasted throughout the 4-h observation period. After sodium nitrite doses of 5.5 mg/kg, responses to conditioned inhibition showed only a tendency to motor disinhibition. These results can be explained in terms of the ability of sodium nitrite to inhibit the function of GABAergic receptors, as development of internal inhibition is accompanied by increased inhibitory hyperpolarization processes in which the GABAergic mediator system is involved. The lower and higher sodium nitrite doses produced no increases in myogram amplitudes in responses to combinations of flashes of light and pain reinforcement, as occurred when these stimuli were presented to controls.