PUR POSE The aim of the present study was to determine the effective dose of Carbamazepine . according to the serum level concentration. ° METHODS 20 patients with symptomatic focal epilepsy: 10 males and 10 females included in the study. The average age was 3I.8± 8.9 (range 16-50 years).The mean duration of partial seizure was 11.4 ±5.8 years. All patients were using inappropriate doses of Carbamazepine and most of patients were taking it irregularly. Patients were follow- upped during 3 months. Initial dose of treatment was 9.4 ± 2.2 mg/kg. Pharmacokinetic analysis was performed by ABBOTT TDXFLX immunofluorescence autoanalyser in the Laboratory department of the Central Clinical Hospital. The blood samples were collected from patients in the morning before taking the morning dose and after 2 hours. RESULTS Therapeutic effective serum level of Carbamazepine in 8 seizure free patients (40%) was 8.25 ±2.11 ng/ml (range 6.89- 10.77), daily average dose I0.63±2.57mg/ kg. Adverse effects were observed in 7 patients. Average side effect dose was 14.0 ±3.3 mg/kg and 1275±125 mg (p<00l), serum level was 9.4±2.2 ng/ml. One patient had skin rash, drowsiness, ataxia, tremor, diplopia, vomiting and headache. However those syndromes were disappeared when dose of the drug was reduced. Adverse effects registration was performed. Key words: carbamazepine. therapeutic drug monitoring, partial CONCLUSIONS seizure our results clearly demonstrates that is no difference of the response of Carbamazepine between Mongolian patients and patients from other Asian and Western country. The study has been approved at ^20/6 meeting of Biomedical Ethics Committee in 16 Jun 2005.