Elevated cytokine response has been reported in patients with epileptic seizures. The objective of this study was to investigate the possible role of interleukin-6 (IL-6) in the pathogenesis of infantile spasms in West syndrome (WS). We measured IL-6 levels in cerebrospinal fluid (CSF) obtained from the newly diagnosed patients with WS. Twelve patients with WS (Group I) were classified as symptomatic WS (Group IA) in eight and as cryptogenic WS (Group IB) in four. The results were compared with control groups including patients with tonic-clonic seizures associated with two different kind of inflammation of central nervous system; Group IIA (infection): bacterial meningitis/encephalitis and Group IIB (trauma): post-traumatic seizures. There was no statistically significant difference between the mean values of CSF IL-6 levels in patients with WS (2.95 +/- 2.31 pg/ml) and those of subgroups of WS (Group IA: 2.26 +/- 2.01 pg/ml and Group IB: 4.33 +/- 2.52 pg/ml). Both control groups had highly increased IL-6 levels in CSF (Group IIA: 193.05 +/- 185.52 pg/ml and Group IIB: 112.74 +/- 167.44 pg/ml) than those of the patients with WS. Elevated IL-6 response in patients with tonic-clonic seizures associated with inflammation of central nervous system might be due to the seizures themselves or related to the underling etiology (infection or trauma). However, no elevated IL-6 response was found in patients with infantile spasms.