The effect of morphine and phentanyl on the potentials in the cortex of the large hemispheres, thalamus and midbrain developing with different modes of the dental pulp stimulation was studied in cats. Morphine (1--2.5 mg/kg) and phentanyl (0.05--0.1 mg/kg) above all bring down the potentials amplitude in associative and nonspecific structures with rhythmic stimulation and eliminate post-activation relief. With the morphine donse rising to 2.5--10 mg/kg and that of phentanyl--to 0.1--0.2 mg/kg the responses in mono-and bipolar, sub- and supramaximal and paired stimulation become weaker. With these types of stimulation the potentials amplitude decreases roughly in the same measure. The evoked responses in specific afferent pathways experience less marked changes than do potentials in the associative and nonspecific structures.