The effect of purified toxin obtained from the venom of the Brazilian scorpionTityus serrulatus on the small and large granular vesicles and on the large agranular vesicles of the Auerbach's plexus of the rat was investigated. Two segments of the rat ileum were immersed in an isolated organ bath containing Jalon's solution and toxin (15μg/ml) was added to one of these baths (9 exps.). The vesicles were counted in 1300 transversely cut axons and the number of vesicles per 100μ2 of axonal area was estimated. The toxin did not produce any change in the morphology of the vesicles, but differences in the distribution of the vesicles were found. In the treated group a decrease in the number of the granular (dense) vesicles and an increase in the number of the agranular vesicles was observed. Our findings suggest that granular vesicles contain catecholamines and substance P, and that scorpion toxin by releasing both substances, decreases the number of these vesicles.