The effects of zonisamide (3-sulfamoylmethyl-1,2-benzisoxazole), a novel anticonvulsant, on extracellular levels of monoamine and its metabolite in the striatum and hippocampus, and Ca2+ dependent monoamine release in the striatum of freely moving rats were studied by microdialysis. Zonisamide increased dopamine, homovanillic acid and 5-hydroxyindoleacetic acid, and decreased 3,4-dihydroxyphenylacetic acid in the rat striatum. However, zonisamide showed no effect on Ca2+ dependent dopamine release in the rat striatum. In the hippocampus, zonisamide increased dopamine, homovanillic acid, serotonin and 5-hydroxyindoleacetic acid and decreased 3,4-dihydroxyphenylacetic acid. The present results suggest that zonisamide facilitates dopaminergic and serotoninergic neurotransmission but does not affect Ca2+ dependent dopamine release within therapeutic plasma concentrations.