Both the cerebellum and the basal ganglia have been associated with the predictive and reactive anticipation of forces and torques. However a comparison between the different findings is difficult. We investigated grip force stabilisation under predictable and un-predictable loading conditions in patients with dysfunction of the cerebellum and of the basal ganglia. Subjects held a manipulandum with a force transducer measuring the grip force and the orthogonal load force. A sinusoidal load force profile was produced by a motor (external condition), or the load was produced actively by the subject either against a fixed resistance (isometric condition) or by up-and-down movements of the manipulandum (inertial condition). Grip force levels as well as the coupling between the grip and load force were evaluated. Twenty-four patients with degenerative cerebellar diseases and 22 patients with PD were tested. Cerebellar patients as well as PD patients produced exaggerated grip forces in all three conditions compared to healthy control subjects. As had to be expected, the grip force lagged load force in the external condition. In the self-generated conditions the delay was generally around zero indicating that subjects of all groups modulated the grip force in feedforward manner. However, the coefficient of cross-correlation, which quantifies the precision of force coupling, was clearly decreased in the cerebellar patients in all tasks. In contrast, the coefficient of PD patients was normal irrespectively from the task. Cerebellar and PD patients exhibited similar deficits of force economy obvious as increased grip forces. In contrast, only cerebellar patients exhibited impaired force coupling irrespectively from the type of force production. The findings suggest that the cerebellum is involved in the stabilization of force against perturbations that may either be self-produced or being externally produced. The basal-ganglia seem to have no a major role in this aspect of force control. Funded by the Deutsche Forschungsgemeinschaft