Cognitive and psychomotor impairments can be unwanted adverse effects of antiepileptic drugs. The present double-blind, cross-over study with healthy volunteers was designed to assess the effects of two doses of oxcarbazepine (OXCZ) (150 mg b.i.d.; 300 mg b.i.d.) and a placebo, each given over a two week period. Twelve subjects completed a battery of tests before and 4 h after morning doses on days 1, 8 and 15. Results of objective tests indicated that OXCZ improved performance on a focussed attention task and increased manual writing speed. Subjective ratings showed OXCZ increased feelings of altertness, clear-headedness and quickwittedness. OXCZ had no effect on the range of long-term memory processes assessed in this study. It is concluded that at the doses employed, OXCZ has a slightly stimulant effect on some aspects of psychomotor functioning.