To investigate pulmonary function abnormalities in Parkinson's disease (PD), we obtained maximal inspiratory and expiratory flow-volume curves in 63 patients (59 under treatment) with different stages of the disease, not filtered for respiratory symptoms. PD severity was evaluated by the Unified PD Rating Scale, the Webster's scale, and Hoehn and Yahr staging. Patients with more severe PD had lower percentage forced vital capacity (FVC%), and peak inspiratory and expiratory flows. Those with fluctuations and/or dyskinesias had lower FVC% and percentage forced expiratory flow volume in 1 sec (FEV1%). There were a number of weak but significant correlations between PD scales and spirographic parameters. Thirty one patients (49.2%) had pathological flow-volume curves. The clinical profile and the duration of the disease did not influence the pattern of the curve. Physiologic evidence of upper airway obstruction was observed in 3 cases. A spirometric restrictive ventilatory defect (FEV1/FVC higher than or equal to 80%) was observed in 54 patients (85%), while generalized airway obstruction was present only in one nonsmoker. We conclude that abnormal flow-volume loop contour is a frequent finding in PD. This probably reflects involvement of the upper airway musculature, that in some patients can produce upper airway obstruction. Generalized airflow limitation is not an important characteristic of PD. By contrast, a restrictive spirometric defect, probably due to incoordinated expiratory effort or abnormally low chest wall compliance, is the main spirometric finding in these patients.