Simple reaction time lengthens in parkinsonian patients as the severity of motor disorder progresses. Shortening of reaction time was obtained by giving a warning signal to a greater extent in cases with severer motor disability. The results suggest that inattention, one of several symptoms common to lesions in the frontal lobe and Parkinson's disease, may be a factor in bradykinesia in purposive movements in the disease. The Wisconsin card sorting test and criterion shift task which we devised to deal with a single patients have difficulty in dealing with multiple sets simultaneously, which may be caused also by inattention. In execution of ballistic movement in parkinsonian patients, only a small torque constant in amount and in time can be produced in the beginning, irrespective of the size of force required, and subsequently enough force is built up to reach the target. This was more marked in cases with severe motor disability and in cases with decrease in power. Rigidity, mechanical properties of the limb or disorders in ocular movement were not responsible for the production of the initial small torque. Oculo-manual incoordination in visuomotor tracking tasks is also discussed.