"Endozepines" are endogenous ligands for the benzodiazepine recognition sites on gamma-aminobutyric acid A receptors in the nervous system. Idiopathic recurring stupor (IRS) is a syndrome of spontaneous stupor or coma that is not associated with known metabolic, toxic, or structural abnormalities but can be reversed by flumazenil, a pure benzodiazepine antagonist. We measured endozepine-2 and endozepine-4 by high-performance liquid chromatography and radioreceptor assay in serum and cerebrospinal fluid from three patients with IRS. During episodes of stupor there was a large (up to 300-fold compared with control patients) increase of endozepine-4 content in cerebrospinal fluid and serum, but a return to normal concentrations between attacks. Endozepine-4 may contribute to, or be the cause of, IRS. The reasons for abnormal concentrations of endozepine in blood and brain are unknown.