In 18 healthy age- and sex- matched controls and 13 patients with Wilsons disease (18-50 years) under continuous copper chelating therapy sinusoidal forearm movements of a given target rates (target rates: 0.2, 0.3, 0.4, 0.5, 0.6 Hz) as well as breathing movements were recorded by means of a goniometer and a breathing girdle in parallel. Additionally, controls and patients had to perform spontaneous forearm movements at their most comfortable rate. The percentage of time during which forearm and breathing movements were coupled was significantly reduced in the patients. With increasing target rate the mean breathing rate significantly increased in the controls but not in the patients. Furthermore, the variability of breathing rate significantly increased in the patients but not in the controls. These two factors probably caused that the coupling of breathing and extremity movements was significantly reduced in the patients.