A modified grip strength meter was designed to enable the separate measurement of lateralised grip strength in the two forelimbs of rats, in order to allow assessment of deficits in animals with unilateral lesions and grafts within the basal ganglia. Unilateral 6-hydroxydopamine lesions of the dopaminergic nigrostriatal bundle induced a significant asymmetry, marked by an increased grip strength on the side contralateral to the lesion. Lesioned animals with additional implants of embryonic nigral cell suspensions into the dopamine-denervated neostriatum showed a reduced (but not significant) deficit and did not differ from control performance. The lateralised nature of the deficit excludes explanation based on global activational changes; rather the unilateral deficit may provide a simple test of unilateral `rigidity' in a widely used rodent model of Parkinson's disease.