The psychoneuroendocrinology of schizophrenia derives from the presumption that neurotransmitter or receptor abnormalities in the limbic regions might extend to or influence the hypothalamus, which plays a role in the regulation of prolactin (PRL) secretion from the anterior pituitary gland. Since a GABA disturbance has been recently proposed in the pathogenesis of certain schizophrenic symptoms, and since a tuberoinfundibular-GABA (TI-GABA) system has been shown to modulate PRL secretion in humans, we tested the activity of this system both in controls and in chronic schizophrenic women. For this purpose the GABAergic drug sodium valproate (800 mg) was administered orally to 20 healthy women and 18 chronic schizophrenic women. Plasma PRL levels were measured before and after the drug administration. Sodium valproate decreased PRL concentrations only in the healthy women. Although the hypothesis of a GABA disturbance in schizophrenia at present is only speculative, these results might suggest a defect of the TI-GABA system in chronic schizophrenia.