Our earlier biochemical studies suggested that the neurosteroid pregnenolone sulfate (PS) may reduce gamma-aminobutyric acid (GABA) action at the Cl- channel associated with GABAA receptors. In the present electrophysiological study the interaction of PS with the GABAA receptor was tested, using whole-cell voltage-clamp recordings from isolated cerebral cortical neurons of neonatal rats. At micromolar concentrations PS reversibly inhibited GABA-induced current, behaving as an allosteric receptor antagonist.