In 14 children with epilepsy, 51 with febrile convulsions and 22 with meningitis gamma-aminobutyric acid (GABA) concentrations in lumbar CSF were determined. While the mean for CSF GABA concentrations for all epileptic children was unchanged [144 (range: 73-285) pmol/ml; controls: 148 (range: 90-243) pmol/ml] extraordinarily high GABA levels were found in the CSF of two children on valproate (525 and 557 pmol/ml) and remarkably low GABA concentrations in hitherto untreated epileptic children [109 (range: 67-176) pmol/ml]. Children with febrile convulsions [103 (range: 63-170) pmol/ml] and acute meningitis [105 (range: 65-171) pmol/ml] had significantly decreased CSF GABA concentrations (P less than 0.001 and P less than 0.02 compared with controls). The data indicate that valproate intake increases dramatically the GABA concentrations in the CSF of epileptic children. Furthermore, the study supports the concept that low GABAergic activity within the CNS may be one cause for an increased seizure frequency.