Bromocriptine, a preferential D2 receptor agonist, was administered to six human narcoleptic patients during a double-blind, cross-over study. Laboratory sessions consisted of two all-night polysomnographic recordings and three daytime tests of vigilance: the Analogue Vigilance Scale (AVS), the Maintenance of Wakefulness Test (MWT), and the Four-Choice Reaction Time Test (FCRTT). No change in nocturnal sleep organization, daytime somnolence, or psychomotor performance was observed during bromocriptine administration. Periodic limb movements in sleep (PLMS) were significantly reduced during bromocriptine condition. These results suggest that D2 receptors are unlikely to play a major role in the physiopathology of human narcolepsy, and support the hypothesis that dopaminergic mechanisms are involved in PLMS.