The effects of optokinetic stimulation on the disorders of position sense in the horizontal and vertical planes were assessed in 24 patients with unilateral cerebral lesions (eight right brain-damaged patients with visuo-spatial hemineglect, eight right brain-damaged patients without neglect, eight left brain-damaged patients without neglect). In neglect patients, the position sense disorder was more severe, and affected by optokinetic stimulation in a direction-specific fashion. In both the horizontal and the vertical plane, and in both arms, stimulation with a direction of the movement contralateral to the side of the lesion improved the disorder, whereas stimulation with an ipsilateral direction worsened the deficit. The suggestion is made that in patients with neglect the disorder of position sense is produced, at least in part, by an ipsilateral distortion of an egocentric co-ordinate system, comprising both the horizontal and the vertical dimension, which may be affected by direction-specific optokinetic stimuli.