We studied 153 patients with partial epilepsy who were placed on a carbamazepine monotherapy plan in order to evaluate the clinical factors that may determine drug responsiveness to carbamazepine. The subjects were divided into 3 groups based on their therapeutic outcome--complete seizure control (44%), significant seizure reduction (32%) and unsatisfactory control (24%). Fifteen tentative clinical factors were examined in relation to the therapeutic outcomes. Factors such as seizure type, number of generalized tonic-clonic seizures, age of onset, duration of illness, seizure frequency, previous treatment and EEG finding were relevant to drug responsiveness. However, other variables including mental retardation, etiology, febrile convulsion, positive family history and abnormal neurologic examination showed no significant correlation. Our data suggest that a potential success of carbamazepine treatment should not be underestimated even in patients with complicated clinical features.