We report two patients with slowly progressive motor disorders, whose principal manifestations were asymmetric limb-kinetic apraxia and muscle rigidity. In both patients MRI revealed no responsible lesion, whereas single photon emission computed tomography (SPECT) showed a decrease in cerebral blood flow (CBF) in the unilateral hemisphere. One patient with mainly right-sided apraxia had a decreased CBF in the left central region between the frontal and parietal cortices, and the other patient with left-sided apraxia in the right parietal cortex. In agreement with asymmetric clinical symptoms, the regional CBF decrease in the unilateral cortical areas including the frontal and parietal cortices may suggest a degenerative disease, presumably diagnosed as having cortico-basal degeneration.