We used positron emission tomography (PET) to investigate which cortical motor areas are active in relation to unilateral dominant or non-dominant finger movements in left-handed subjects. The right premotor area was activated by both contralateral and ipsilateral finger movements, in contrast to the primary motor, the left premotor and supplementary motor areas in which activation was only by contralateral movements. Bilateral finger movements activated all of these areas. We conclude that there exists cortical asymmetry for motor control in left-handers which is different from that apparent in right-handers.