In both clinical and laboratory tests, patients with Parkinson's disease have considerable difficulty in performing different manual tasks simultaneously with the two hands. The present study reports on an unusual enhancement in performance under such conditions in a substantial proportion of patients tested. When performed at the same time as repetitive tapping tasks, the ability to rapidly place pegs in holes improved in almost half of the patients compared with unimanual performance of the peg task. Various possible explanations are considered for this unusual finding. The two most plausible, and testable, relate to either the withdrawal of attention from the task permitting a more automatic mode of execution, or a facilitation provided by sensory feedback from the simultaneous tapping task.