It has been shown that Fasciculins (FAS), polypeptides isolated from the venom of the green mamba Dendroaspis angusticeps, provoke a powerful inhibition of peripheral acetylcholinesterase (AChE). In the present study, 0.5 microliter of increasing concentrations (10-500 micrograms/ml) of FAS were injected into the striatum of rats. Micropunches taken 2 mm around the injection site showed 90% inhibition of AChE up to 24 h after FAS injection (500 micrograms/ml). AChE activity was about 50% of controls at the 7th day without apparent cell loss. Assessment of AChE activity in the whole striatum showed no inhibition. It is postulated that, due to this potent, localized and long-lasting central nervous system AChE inhibition, FAS could become a useful tool for the study of central cholinergic pathways.