Patients with Parkinson's disease may have more difficulty performing repetitive motor acts than single motor acts because of bradykinesia and skeletal muscle rigidity. We thought that repetitive ventilatory tasks might be similarly limited and that this dysfunction would likely contribute to respiratory muscle fatigue. We studied 9 patients with Parkinson's disease who had no evidence of restrictive or obstructive lung disease and 5 normal age-matched control subjects who performed repetitive, forced inspiratory resistive-loaded tasks. The time a given mean airway opening pressure could be sustained, the incremental oxygen cost of breathing, and the work rate of breathing (W) were measured. Although maximal static inspiratory pressures were comparable in both groups, 8 of the 9 patients could not sustain as high a W in the resistive-loaded tasks as could the normal control subjects (41.0 +/- 23.0 versus 67.7 +/- 29.1 J/min; mean +/- SD, p less than 0.01) and the efficiency of breathing was reduced (2.0 +/- 0.8 versus 3.8 +/- 1.4%; p less than 0.01). These findings are similar to derangements of task performance by peripheral skeletal muscle groups in Parkinson's disease.