Determining antiepileptic drug (AED) concentration in biological fluids and calculating its dosage on this basis is a long-term method in the treatment of epilepsy. This facilitates the treatment and increases the safety of patients in the aspect of suitable seizure control and reduced risk of side effects. This report presented the range and the number of antiepileptic drug concentration determined during thirteen years activity of Laboratory of Clinical Neuropharmacology in the Department of Developmental Neurology. There was also a number of drug concentrations particularly often determined presented, compared and discussed. Moreover, there were also analyses of subtherapeutic, therapeutic and potentially toxic concentration decomposition presented for subsequent AEDs. The frequency of conventional drug and of slow released forms for VPA and CBZ was compared. VPA appeared to be the most frequently monitored drug and CBZ occurred to be the next one. The concentrations of PHT, PB, PRM and ETH were more rarely determined. In the observed period of time the number of LPP concentration determined in the therapeutic range amounted to 69%, the least frequently the potentially toxic levels were determined--11%. Normal concentrations i.e. therapeutic ones were most often determined for CBZ (77%) and subtherapeutic levels were determined mostly for PHT.