It has been known that carbamazepine (CMZ) induces the hepatic microsomal enzymes. Increased hepatic plasma clearance causes a change in the serum concentration of thyroid hormones. The effect of CMZ monotherapy on thyroid functions in 42 cases having partial epilepsy (17 male, 25 female) was compared with the result of normal control group of 21 cases. The mean age of the cases was 32 (range:15-72), the mean duration of seizure period was 9 (1-34) years, the duration of CMZ use was 4 (1-9) years. The serum level of free T-3 (FT3) was 2.92 Pg/ml, FT4: 1.38 Ng/ml, T-3: 125.1 ng/ml, T-4: 6.76 Ug/ml, TSH: 2.06 mIU/ml in the patient group. FT3 was 2.40.Pg/ml, FT4: 1.01 Ng/ml, T-3: 120.38 ng/ml, T-4: 6.07 Ug/ml, TSH: 2.04 mIU/ml in the control group. Serum FT3 level was found to be significantly higher in the cases administering CMZ when compared to control group (p: 0.006). Changes in the FT4 and FT4 serum levels were found to be insignificant. CMZ did not cause any change in serum level of TSH (p: 0.218), The duration of using antiepileptic drugs did not change the levels of thyroid hormones (p: 0.718). The thyroid ultrasonography and scintigraphy of cases were found to be normal.