Rapid, self paced and self terminated elbow flexion movements were studied in a group of 10 patients with dystonia affecting the arms. The movements were slower and for small amplitude movements, more variable than those recorded in normal subjects. The duration of the first agonist burst was prolonged, even when compared with normal subjects deliberately moving slowly. Cocontraction of agonist and antagonist muscles during ballistic movements was common and may contribute to the bradykinesia. These findings are compared with similar studies of other diseases of the motor system. Unlike many other conditions which also reduce the speed of ballistic voluntary movements, the patients with dystonia in the present study showed a normal symmetry of acceleration and deceleration times. One interpretation of this finding is that aspects of the basic motor programmes are relatively preserved in this condition and account for the surprising retention of motor skills shown by some patients with dystonia.