In the experiments on non-anesthetized flaxedil-immobilized cats it has been shown that the injection of leucin-enkephalin (1 mg) into the lateral ventricle of the brain is followed by the inhibition of evoked potentials in the ventrolateral columns of the spinal cord and of segmental interneuronal transmission in the spinal cord as well as by the reduction of the amplitude of potentials in the S I zone of the brain cortex induced by the sciatic nerve stimulation. Naloxone (1 mg/kg, i.v.) prevented the effects of leucin-enkephalin. Methysergide pretreatment (2.5 mg/kg, i.p.) led to a decrease of leucin-enkephalin effect on the interneuronal transmission in the spinal cord. Leucin-enkephalin failed to change the amplitude of polysynaptic potentials of glosso-mandibular reflex integrated at the brain stem level.