Dendrotoxin was isolated from green mamba (Dendroaspis angusticeps) venom and its effects on motor behavior and cortical and subcortical bioelectrical activity were studied in the rat. In chronic experiments, free moving rats injected i.p. with dendrotoxin, presented motor behavior similar to that described in rat amygdaloid epilepsy and bioelectrical signs of epilepsy beginning at the amygdala were observed. In acute experiments, rats anaesthetized with urethane were intracerebrally or intracerebroventricularly injected with dendrotoxin, which produced bioelectrical signs of epilepsy. Following intracerebroventricular injection, signs of epileptic discharge were first observed at the dorsal hippocampus. When dendrotoxin was microinjected in the amygdala or the hippocampus, the seizures appeared at the injection sites with a shorter latency and the bioelectrical epileptic signs lasted longer than when injections were given in non-limbic structures, such as the globus pallidus or the mesencephalic reticular formation. Dendrotoxin is a very powerful toxin that acts effectively at the level of the limbic system.