Excessive daytime sleepiness (EDS) may limit the symptomatic treatment of Parkinson's disease and can alter the patient's lifestyle significantly. Ten consecutive patients with Parkinson's disease on various dopaminergic drugs and EDS were recruited to a 4-week open-label trial of modafinil. Patients were evaluated using the Epworth Sleepiness Scale and Unified Parkinson's Disease Rating Scale part III. All but three patients, with previous history of intolerability of a dopamine agonist caused by EDS, remained on their baseline medications. Modafinil was titrated as needed to a maximum of 400 mg/day. The mean Epworth Sleepiness Scale score at baseline of patients completing the study (n = 9) was 14.22 (+/- 3.03). After completing the study on an average dose of 172 mg/day, the Epworth Sleepiness Scale score was 6.0 (+/- 4.87). Unified Parkinson's Disease Rating Scale scores were not affected by this medication. Side effects encountered were headache, generalized paresthesias, and hallucinations (n = 1 each, the patient developing hallucinations dropped out of the trial before completing 4 weeks of the study drug). The three patients who did not tolerate any increments of dopamine agonist before modafinil were able to tolerate further upward titration of the dopamine agonist. Modafinil may be effective in reducing EDS in patients with Parkinson's disease treated with dopaminergic drugs. It does not seem to worsen parkinsonian symptoms and may allow further increase in dopaminergic therapy in patients previously unable to tolerate this because of EDS.