A variable structure system (VSS) control paradigm has been applied to the investigation of the neurophysiological control of limb movement. The adoption of this nonlinear model structure was suggested both by previous results obtained with a linear black box model and by theoretical considerations about the relevance of nonlinear control theory for the study of limb movement control. The reaching-to-grasp and pointing movements have been studied. A nonlinear state observer connected to the controller has been introduced, in order to estimate the angular velocities necessary to the controller itself. The proposed nonlinear controller model has been experimentally identified. As a general result, a VSS model structure has been found satisfactory in almost every case.