There has been increasing recognition of pre-motor manifestations of Parkinson's disease (PD) resulting from early brainstem involvement. We sought to determine whether ventilatory control is abnormal. Patients with PD without respiratory disease were recruited. Spirometry, lung volumes, diffusing capacity and respiratory muscle strength were assessed. Occlusion pressure and ventilation were measured with increasing CO2. Arterial blood gases were taken at rest and following 20 min exposure to 15% O2. A linear correlation assessed associations between respiratory function and indices of PD severity. 19 subjects (17 males) with mild-moderate PD were studied (mean (SD) age 66 (8) years). Respiratory flows and volumes were normal in 16/19. Maximum inspiratory and expiratory pressures were below LLN in 13/19 and 15/19 respectively. 7/15 had a reduced ventilatory response to hypercapnia and 11/15 had an abnormal occlusion pressure. There was no correlation between impairment of ventilatory response and reduction in respiratory muscle strength. Response to mild hypoxia was normal and there were no associations between disease severity and respiratory function. Our findings suggest that patients with mild-moderate PD have abnormal ventilatory control despite normal lung volumes and flows.