The aim of the study was to verify the role of gamma-aminobutyric acid in the pathogenesis of hepatic encephalopathy occurring in cirrhotic patients by attempting to correlate plasma and cerebrospinal fluid content of authentic gamma-aminobutyric acid with the neurological manifestations of hepatic encephalopathy. For this purpose, plasma and cerebrospinal fluid gamma-aminobutyric acid levels were measured by means of mass fragmentography in 17 cirrhotic patients with hepatic encephalopathy and in 6 cirrhotics without neurological symptoms. Moreover, in all patients, a second sample was obtained during the clinical course of hepatic encephalopathy. The mean plasma and cerebrospinal fluid gamma-aminobutyric acid levels were not different in patients with or without hepatic encephalopathy and did not change during the evolution of the neurological symptoms. The lack of changes in the gamma-aminobutyric acid content in plasma and cerebrospinal fluid during hepatic encephalopathy is in contrast with the hypothesized importance of increased entry into the brain of gamma-aminobutyric acid in the pathogenesis of hepatic encephalopathy.