Serum concentrations of total carnitine, free carnitine and acylcarnitine were measured in forty-one epileptic patients treated with valproic acid (VPA). Among them, 14 patients were on VPA monotherapy and 27 were on VPA polytherapy. Forty-one age and sex matched healthy normal controls were also evaluated for carnitine metabolism. The mean total and free carnitine were significantly lower in both the VPA monotherapy and polytherapy groups compared with the controls. However, there were no significant differences in concentrations of carnitine between the VPA polytherapy and VPA monotherapy groups. Patients treated with VPA polytherapy had lower carnitine than those treated with VPA monotherapy. An inverse correlation was found between serum concentrations of carnitine and duration of treatment in patients treated with VPA. However, there was no significant correlations between serum concentrations of carnitine and those of VPA. Also, correlation between serum concentrations of carnitine and the activities of serum GOT and GPT was not significant. After L-carnitine supplementation in eleven patients with hypocarnitinemia, the concentrations of carnitine were significantly increased.