Epilepsy is the most common neurologic disorder of childhood. In approximately 6-14% of all patients with epilepsy, complete seizure control is difficult to achieve with current antiepileptic treatments. Several current studies have shown in both animals and people that the lengthening of epileptic seizures and frequent recurrence increases the likelihood of neuronal damage. S-100B protein is the most analyzed brain derived peripheral biochemical marker in brain damage. This study aimed to evaluate interictal serum S-100B protein levels in children diagnosed with intractable epilepsy. A group of 32 patients with intractable epilepsy and 25 healthy controls were recruited. Serum S-100B protein levels were measured using a commercially available electrochemiluminescence immunoassay (ECLIA kit, as supplied and according to the manufacturer's standards. The serum S-100B protein levels of the patient group in the study were found to be 0.094 +/- 0.011 mu m/L, and 0.083 +/- 0.014 mu m/L in the age-matched control group. The difference between the groups was determined to be statistically significant (P = 0.004). In conclusions, it can be said that as the serum S-100B protein levels of the patients with focal epilepsy were high compared to those of the control group, this can be reliable peripheral biomarker for neuronal damage in patients with focal intractable epilepsy. (C) 2013 Elsevier Ireland Ltd. All rights reserved.