Measurement of the serum levels of antiepileptic drugs is an important progress in managing the patients with epilepsy. The determination of serum levels has become indispensable in special indications such as assessing the compliance in taking medication and identifying the responsible agent in intoxicated patients on multiple drug therapy. The long-term prognostic value of the routine determination of anticonvulsant drugs is related to the validity of the concept "therapeutic serum level".