Biological effects of tiagabine, a new antiepileptic drug, were analyzed on cultures of rat's cortical astrocytes. Tiagabine was added to the cultures at concentrations of 1 and 10 microg/ml, correspondent to therapeutic range; cell viability (tetrazolium salt assay and lactic dehydrogenase release), maturation and differentiation (glutamine synthetase activity) and presence of stress conditions (reactive oxygen species formation, inducible nitric oxide synthetase expression and 70 kDa heath shock protein production) were tested. Our results indicate that the addition of Tiagabine to primary astrocytes not only did not change significantly the examined metabolic activities but also seems to exert a protective action against oxidative stress. Thus, our data reinforce the idea that Tiagabine may be considered an effective promising drug in the treatment of epilepsy.