Incidental case reports suggest that some parkinsonian patients treated with dopamincrgic drugs complain of drowsiness but few controlled data are available. We compared the sedative effects of L-Dopa (200 mg + 50 mg benserazide, PO), triazolam (0.125 mg) and placebo in a randomized double-blind cross-over design in 22 healthy volunteers pretreated with domperidonc (60 mg/day). Drowsiness was assessed using a visual analog scale (VAS), a computerized choice reaction time test (CRT) and an electro-oculogram (EOG). L-Dopa and triazolam induced significant drowsiness, compared to placebo, on VAS, CRT and some EOG parameters. After this first evaluation session, all subjects were chronically treated for 11 days with 600 mg/d of L-Dopa. Drowsiness induced by L-Dopa, triazolam or placebo was then tested again on three consecutive days to assess putative dopaminergic tolerance. After chronic L-Dopa treatment, triazolam-induced sedation remained unchanged while L-Dopa sedative effects were no longer significant except on the VAS, preventing the conclusion that tolerance occurred. These data suggest that an acute dose of L-Dopa induces sedation in L-Dopa-naive subjects. This sedative effect must be considered in clinical practice and when studying the effects of L-Dopa on motor or neuropsychological performance, especially in acute tests.