Modafinil (CRL 40476) is a recently developed central alpha adrenergic agonist with vigilance-promoting properties. In a double-blind, placebo-controlled sleep laboratory study, its single-dose effects on objectively and subjectively evaluated sleep, morning awakening, and early morning behaviour were investigated and compared with amphetamine. Ten young healthy volunteers of both sexes spent 12 nights in the sleep laboratory: one adaptation night, one baseline night, five drug nights (100 mg and 200 mg modafinil; 10 mg and 20 mg d-amphetamine; placebo) and five subsequent washout nights. The drugs were administered in one week intervals according to a Latin square design. Somnopolygraphic investigations were performed between 22h30 and 06h00. Subjects received the drug orally half an hour before bedtime. A self-rating scale for sleep and awakening quality and early morning behavior was completed subsequent to the morning toilet. Thereafter, noopsychic and thymopsychic variables were evaluated utilizing a psychometric test-battery. Statistical analyses of objective sleep variables demonstrated that modafinil causes no significant changes as compared to a placebo. Sleep initiation remained unchanged after all of the drugs, while sleep maintenance was impaired dose-dependently after d-amphetamine. Thus, total sleep time and sleep efficiency decreased significantly after 20 mg d-amphetamine as compared to the placebo and modafinil. In regard to sleep architecture a reduction of sleep stage 2 and rapid eye movement-sleep occurred under d-amphetamine while modafinil did not exhibit such an effect. Subjective sleep quality was significantly better after modafinil than after the reference compound. Subjective awakening quality and well-being in the morning did not show any significant findings. Furthermore, no differences were observed between the placebo and the other drugs concerning objective awakening quality (evaluated by psychometric tests). Critical flicker frequency increased significantly after 20 mg d-amphetamine as compared to the placebo. Pulse rate and evening and morning blood pressure remained unchanged. These data stress the necessity to differentiate between "vigility-increasing" properties of amphetamine and "vigilance-promoting" properties of modafinil.