Abstract: The effects of corydalis B and chlorpromazine on the descending influences of different areas of the brain stem reticular formation (RF) upon flexor reflex activities were studied in 47 chloralose anesthetized cats. Corydalis B (15—20 mg/kg) showed a powerful blocking action on the inhibition evoked by stimulating points in the inferior olivary nucleus (IO) and superior olivary nucleus (SO)of the medulla oblongata. It also exhibited a blocking action on the facilitation induced by stimulating the areas of nucleus gracilis (NG), medial RF and central tegmental tract. But the facilitation evoked by stimulating points in the decussation of the brachium conjunctivum (DBC) and substantia nigra ventral was unaffected. Under the influence of large doses of corydalis B, a reversal into facilitation of inhibition of spinal flexor reflex induced by stimulating the IO or SO was sometimes also observed. Chlorpromazine (0.5—1 mg/kg) blocked the inhibition elicited by stimulating the inhibitory points in the medial longitudinal fasciculus and the facilitation induced by stimulating the facilitatory points in the NG at the medulla oblongata. In the same experimental conditions the inhibition produced by stimulating the IO and the medial lemniscus at the level of medial aperture of the 4th ventricle remained unchanged. The facilitation evoked by stimulating DBC of the midbrain was also not influenced under the action of chlorpromazine. It may be concluded that the actions of corydalis B on descending functions of the brain stem reticular formation are similar to those of chlorpromazine, although their selective sites of action are not entirely the same.