Duvernoy's gland secretions (100 micrograms/ml) from the eastern hognose snake, Heterodon platirhinos, induced a neuromuscular blockade in the isolated frog sciatic nerve-gastrocnemius muscle preparation and effectively antagonized acetylcholine and histamine responses of the rat duodenum preparation. The Duvernoy's secretions (100 micrograms/ml) produced a reversible, excitatory effect in the guinea-pig ileum in vitro. Mice administered the secretions (100 mg/kg, i.p.) exhibited minor, transient signs of toxicity. These preliminary observations provide evidence for toxicity of H. platirhinos Duvernoy's gland secretions but do not warrant categorizing the potential toxicity of this species with that of proteroglyphous, solenoglyphous, or the more venomous opisthoglyphous species.