AbstractRecent work has led to the discovery of six patients with 4‐hydroxybutyric acid‐uria, a severe hereditary human pathology characterized by the accumulation of a compound of known neuropharmacologic activity in body fluids. The enzymatic deficiency has been localized to succinic semialdehyde dehydrogenase, one of two enzymes involved in the metabolism of the neurotransmitter GABA. The disease is inherited as an autosomal recessive trait, and carrier detection has been accomplished by quantification of intermediate enzyme activities. The clinical, enzymatic and pharmacologic characteristics of this disease are reviewed here.