We started the subject screening from over 400 patients with Parkinson's disease using strict selection criteria to identify the patients with nocturia who would allow accurate and efficient evaluation of the pergolide effects. The subjects were confined to female patients to exclude patients with potential prostate hypertrophy. The patients treated with bromocriptine at 7.5-15 mg/day adjunctive to l-dopa were selected to replace bromocriptine with pergolide of the equivalent dosage approved in Japan. The nocturia was defined as having more than two episodes of urination during sleep per night on average. The subjects received the urinary sediment test before and during the study for screening urinary tract infection and the study was discontinued when urinary tract infection was found. As a result, we identified total 11 patients with nocturia and three of those completed the 12-week study of switching dopamine agonist from bromocriptine to pergolide. We observed a decrease in nocturia frequency in all three patients, a decrease in irritative urinary symptoms in two and an improvement of sleep QOL in two. The effect of pergolide on nocturia was independent of improvement of parkinsonian symptoms, suggesting a distinct mechanism from that of anti-parkinsonian effects. Our study also suggests that switching from bromocriptine to pergolide improves nocturia, thereby improving sleep status of patients with Parkinson's disease.