A thrombin-like enzyme, purified from the venom of Crotalus durissus terrificus by gel filtration and affinity chromatography, showed a single protein band in Sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS-PAGE) with a molecular weight of about 33kDa. Clear cellular morphological changes, deep ganglioside level modifications in some brain areas and behavioral alterations in pup rats injected with this protein were detected. Ganglioside composition, one of the chemical markers of brain maturation, was altered specially in the hypothalamus, hippocampus and prefrontal cortex. The most reliable behavioral effects were a delayed, maturation of the righting reflex, posture and motor response after treatment. These effects were consistent with the histological changes revealed in the cerebellum and prefrontal cortex of treated neonate rats, areas related to motor activities.