In an infant with neonatal seizures, CSF GABA levels were determined before and after treatment with vitamin B6. Before onset of treatment, the level of GABA in CSF was very low (13 pmol/ml). Injection of vitamin B6 blocked the seizures immediately. When GABA level in CSF was again analysed after continued treatment with vitamin B6, a value of 127 pmol/ml was determined, which is within the normal concentration range in children. The data substantiate previous findings in brain tissue from a patient with vitamin B6-dependent seizures, and strongly indicate that impairment of central GABAergic activity was the cause of the seizures.