Extracts and secretion of the Duvernoy's gland are venomous, inducing in several cases motor paralysis in experimental animals. The extracts of the Duvernoy's gland from the aglyphous colubrid Dryadophis bifossatus are very toxic, eliciting flaccid paralysis in pigeons, rabbits and Hylae (Brazil and Vellard, 1926). In the present study, the neuromuscular action of the extracts of Duvernoy's gland from this Colubridae was investigated in the chick biventer cervicis nerve-muscle preparation. The muscle was indirectly stimulated with supramaximal purses, and by addition of acetylcholine or carbachol to the organ bath. Direct muscle stimulation was carried out in curarized preparations. The extracts induced an irreversible neuromuscular blockade and also inhibited irreversibly the contracture of the biventer cervicis produced by either acetylcholine or carbachol. The twitches elicited by direct muscle stimulation were not depressed. These results show that the neurotoxin(s) of the extracts interact with the end-plate cholinergic receptors.341011871190Brazil, V., Vellard, J., Contribuição ao estudo das glândulas das serpentes aglyphas (1926) Mem. Inst. Butantan, 3, pp. 301-325Ginsborg, B.L., Warriner, J., The isolated chick biventer cervicis nerve-muscle preparation (1960) Br. J. Pharmac., 15, pp. 410-411Kraus, R., Biologische studien über gift der kopfdrüssen ungiftiger schlangen (1922) München. Mediz. Wochenschrif., 31, p. 1277Kraus, R., Ueber biologische schlangenforchung (1924) Mem. Inst. Butantan, 3, pp. 301-325. , Brazil, V. and Vellard, J. (1926) Contribuição ao estudo das glândulas das serpentes agtyphasLevinson, S.R., Evans, M.H., Groves, F., A neurotoxic component of the venom from Blanding's tree snake (Boiga blandingi) (1976) Toxicon, 14, pp. 307-312Phisalix, M., (1922) Animaux Venimeaux et Venins, 2, pp. 385-395. , Paris: MassonRosenberg, H.I., Bdolah, A., Kochva, E., Lethal factors and enzymes in the secretion from Duvernoy's gland of three colubrid snakes (1985) J. Exp. Zool., 233, pp. 5-14Weinstein, S.A., Kardong, K.V., Properties of Duvernoy's secretions from opisthoglyphous and aglyphous colubrid snakes (1994) Toxicon, 32, pp. 1161-1185Weinstein, S.A., Stiles, B.G., McCoide, M.J., Smith, L.A., Kardong, K.V., Variation of lethal potencies and acetylcholine receptor binding activity of Duvernoy's secretion from brown tree snake, Boiga irregularis Merrem (1993) J. Nat. Toxins, 2, pp. 187-198