Modafinil is a new psychotropic compound with central α1, adrenergic-stimulant activity in animals. In the present study, its pharmacological activity in man was evaluated in the sleep-deprivation induced psychomotor and cognitive impairment paradigm. This was a double-blind placebo-controlled study involving 12 healthy volunteers. Standard psychomotor and memory tasks were used, including critical flicker fusion frequency determination (CFF), choice reaction time and short- and long-term memory evaluation. Results revealed a clear antagonism by modafinil of the psychomotor and cognitive impairment induced by sleep-deprivation in most tasks 6 h after drug administration, and marginal effects 18 h after. These results therefore support a psychostimulant activity of modafinil in man.