Monitoring of valproates is caused by the nonlinear pharmacok-inetics of the drugs and by the clinical effect-concentration dependence. Rapid and simple procedure has been developed to determine valproic acid in the serum and spinal fluid by capillary electro-phoresis. Under the chosen conditions, the calibration curve is linear in the range of concentrations of 10 to 150 mg/1. The detection limit of valproate is 1.0 mg/ml. The accuracy of valproate determination was confirmed by the addition method. The findings were compared by the results of ion chromatographic determination that had been chosen as the reference technique. More than 80 serum samples from patients with epilepsy were analyzed.