To show cortical reorganization in hemiparetic patients with a primary motor cortex (M1) infarct including the precentral knob by using functional magnetic resonance imaging (fMRI).Case-control.Outpatient clinics in the rehabilitation department of a university hospital.Two stroke patients and 20 control subjects.By using fMRI, we evaluated the hand motor function of 2 hemiparetic stroke patients, who had made some recovery from complete paralysis of the affected hand, and 20 control subjects.fMRI was performed by using the blood oxygen level-dependent technique at 1.5 T with a standard head coil. The motor task paradigm consisted of hand grasp-release movements.The contralateral primary sensorimotor cortex was activated by the hand movements of the control subjects and of the unaffected side of the 2 patients. Only the contralateral (infarct side) primary sensory cortex (S1) was activated by the movements of the affected hand of the 2 patients, a result that was not observed in the control subjects or with the unaffected hand in the stroke patients.The hand motor function associated with the infarcted M1 in our patients was reorganized into the S1. These results suggest cortical reorganization in patients with an M1 infarct.