Gamma-hydroxybutyrate administered in anaesthetic doses produced a profound increase in the levels of dynorphin A (DYN) in the hippocampus and pituitary. Simultaneously, a significant, short-lasting decrease in beta-endorphin (B-E) levels occurred in the brain and pituitary. Antiepileptic drugs strongly, though in various ways, influenced the brain DYN and B-E concentrations; though most of them caused a decrease in the hypothalamic opioid peptide content.