1. A pronounced motor asymmetry is observed in rats in the performance of different manipulatory movements of the forelimbs. However, it is not absolute, and depends on a number of factors. 2. The character of the task performed has a fundamental significance for the choice of the limb preferred. The degree of stable preference for one limb is higher in the performance of the most specialized and precise movements. 3. The degree and stability of preference for a certain limb depends also on the length of training in the process of the formation of the given movement. In the process of training, the degree of preference for one limb is least stable in the performance of the most simple movements. 4. Despite the diversity of factors which influence the phenomenon of motor asymmetry, true interhemispheric asymmetry probably also plays a definite role.