To investigate how treatment can affect airway dynamics and respiratory muscle strength in Parkinson's disease (PD), we assessed maximum effort inspiratory and expiratory mouth pressures (MIP and MEP), oscillatory impedance, and maximum expiratory and inspiratory flow-volume curves (MEFV and MIFV) in 10 patients (8 male and 2 female; mean age 51 ± 5.3 yr, SD) after temporary interruption of antiparkinsonian therapy (off) and during continuous subcutaneous infusion of a direct stimulant of dopamine receptors, apomorphine (on). Treatment improved neurologic scores (off 25 ± 5, on 9 ± 5, modified Webster scale, p < 0.001), MEP (off 45 ± 25, on 63 ± 29 cm H2O, p = 0.003), and peak inspiratory flow (PIF; off 3.83 ± 1.6, on 4.37 ± 1.7 L/s, p = 0.028). Maximum inspiratory pressure was very low off treatment (−25 ± 16 cm H2O) and improved moderately with apomorphine (−33 ± 17 cm H2O) (p = 0.064). Total respiratory resistance during tidal breathing was normal in 9 patients both off and on treatment despite, in some cases, dramatic changes in MEFV and MIFV curves. These results suggest that abnormalities of the flow-volume curves may be due to problems in the rapid activation and coordination of contraction of upper airways and chest wall muscles during forced maneuvers, which is improved by apomorphine treatment.