The morphological and histoenzymological changes in the spinal neurons and spinal ganglia of dogs were analyzed after epidural administration of a 2% solution of lidocaine in acute and chronic experiments. In the control group the animals were given epidural infusions of 0.9% saline. The results obtained have shown the absence of pathological structural and metabolic changes in the nervous tissue after lidocaine injection. Certain signs of morpho-functional reorganization were noted in the spinal neurons of animals in both experimental and control groups. The registered changes were found to vary within the physiological fluctuation limits and are rather indicative of the functional reaction of the nervous tissue structures in question to the epidural injections of either saline or lidocaine.