γ-Aminobutyric acid (GABA) has been implicated in the neurochemistry of epilepsy. Lumbar cerebrospinal fluid (CSF) GABA concentrations determined using an ion-exchange fluorometric assay reflect brain GABA content. The mean lumbar CSF GABA concentration among 21 medicated patients with intractable seizures was significantly lower (p < 0.001) than that of 20 urimedicated normal volunteers. Patients with generalized tonic-clonk (grand mal) and complex partial (psychomotor) seizures had significantly lower (p < 0.05) CSF GABA concentrations than those with simple partial (focal sensory/motor) seizures. Although lumbar CSF GABA levels in our seizure patients did not significantly correlate with serum concentrations of phenytoin, phenobarbital, or primidone, additional study of medication-free epileptic patients may be required to evaluate the possibility of anticonvulsant-drug-induced CSF GABA alterations.