CNS stimulants are the most widely used drugs to treat narcolepsy which is characterized by the excessive daytime sleepiness and typically associated with cataplexy. However, a number of side effects may often arise with this therapeutic approach. Thus, investigating new drugs which are efficient but well tolerated is of utmost importance in the treatment of narcolepsy. Although modafinil, an alpha-1 adreno-receptor agonist, has been reported to bring substantial awakening properties in animals, the studies performed in man, particularly in narcoleptic subjects, are few. In the present study, we evaluated the effects of a 300 mg daily dose of modafinil on sleepiness and psychomotor performance of 16 narcoleptic subjects. The major effect of modafinil in narcoleptic subjects was a decrease of daytime sleepiness and corresponding improvement of performances involving attentive functions. However, the learning effect in psychomotor tests may mask the drug effect.