Morphological and quantitative histoenzymological changes in neurons of dog spinal cord and spinal ganglion were studied in acute and chronic experiments with epidural administration of 0.01% clofelin. No morphofunctional changes were revealed after bolus injection of clofelin in a single dose of 6.5 mg/kg. After administration of clofelin in a daily dose of 15 μg/kg for 14 days permeability of capillaries in the nervous tissue decreased at the site of injection, but increased in intact areas. Compensatory changes in energy supply to neurons manifested in activation of aerobic and anaerobic oxidation. Sufficient level of nucleic acids synthesis confirms qualitative validity of nervous cells. Epidural clofelin did not cause dystrophy and necrosis in neurons of the spinal and spinal ganglion.