Kinematic and electromyographic characteristics of step-tracking movements performed with and without visual guidance were investigated in patients with prevalently intermediary and lateral cerebellar and pyramidal tract lesions. Parameters of the phasic programmed component of motion were shown to be little affected by damage to the intermediary cerebellar system, whereas the maintenance phase was severely disrupted and performed as low-amplitude fluctuations around a target level. Lateral cerebellar lesions led to impaired control over the accuracy of the phasic programmed component of motion, a rapid shift into a new position, executed by patients belonging to this group with a constant hypermetric error. Their ability to sustain the position was maintained, however. The phasic component lost its programmatic pattern in patients with pyramidal lesions; the transition to a new position took the form of a slow, fragmented approximation of the limb towards its goal (approximating tracking) in this group, and the maintenance phase was unsteady. Findings are discussed in the light of the theory that the lateral and intermediary systems of the cerebellum are connected with the processes of programming and sustained control of motion, respectively.