Two patients with a slowly progressive and severe motor apraxia are presented. In one case, there was only apraxia; in the other there was moderate memory disturbance and a mild decline of global intellectual ability, suggesting a more widespread cognitive dysfunction. In this second case, recognition of the correct use of objects was also severely impaired, suggesting a disturbance of motor knowledge. In both cases, apraxia was asymmetrical, and associated with a contralateral atrophy of the upper parietal cortex, suggesting a differential involvement of separate action systems for each hand.