Efficacy and safety of lamotrigine (LTG) as add-on therapy was assessed in a randomised double-blind placebo-controlled trial of this drug in 23 adult patients with refractory partial seizures. Fifteen patients showed an improvement on LTG treatment, with a greater than 50% decrease in total seizure count in 7 patients. Fourteen patients experienced fewer simple and complex partial seizures, with 8 patients benefitting by more than a 50% decrease in seizure frequency. The drug was well tolerated over the 2 month treatment period. The plasma concentration of concomitant antiepileptic drugs remained unchanged. No haematological or chemical abnormalities were noted.