Rats (n=11) with bilateral kainate lesions of the caudate nucleus and subsequen unilateral transplantation of embryonic striatal tissue into the damaged area prefered 4 months later to reach for food with the forepaw contralateral to the graft. No such asymmetry was observed in lesioned, nontransplanted (n=8) or unoperated (n=5) control rats. Good integration of the graft with the host brain was indicated by the fnding that cortical spreading depression did not enter the lesioned caudate nucleus but did penetrate into the lesioned caudate with the graft almos as regulary as in intact rats. Behavioral asymmetry produced by unilateral grafts in bilaterally lesioned animals reveals the effects of transplantation with more sensitivity than the graft-induced compensation of the asymmetries caused by unilateral lesions