Tryptophan (Trp), 5-HTP, 5-HT, 5-HIAA, HVA, and MHPG in CSF and total Trp(T-Trp), free Trp(F-Trp) and serotonin in serum were determined in 80 children with epilepsy and also in a control group. It was found that Trp, 5-HT, 5-HIAA in CSF and F-Trp in blood decreased in children with epilepsy. But the decrease of F-Trp was not the main cause of decreased 5-HT metabolism, because the no positive correlations among the four substances were found. Each of them returned to normal levels after the treatment with phenytoin or valproate. 5-HT concentration was negatively correlated with the frequency of the epilepsy episodes. 5-HIAA and HVA levels were relatively higher in the epileptics with brain damage as with compared with those who had no brain damage. The MHPG level was higher in the patients simple partial seizures. Complex partial epileptics and those patients receiving antiepileptic drugs had a lower serum T-Trp level. T-Trp was negatively correlated with the serum valproate concentration. Both T-Trp and F-Trp levels decreased in the patients treated with phenytoin.