The effect of intraventricular fetal mesencephalic grafts placed in the 6-hydroxydopamine (6-OHDA) lesioned striatum on [3H]dopamine (DA) uptake into synaptosomes was studied. Apomorphine (APO)- and amphetamine (AMPH)-induced rotational behaviour was continuously reduced by the grafts over 7 months. After this time, a non-significant increase in [3H]DA uptake into synaptosomes of the lesioned striatum and an approximately 40% decrease in [3H]DA uptake into synaptosomes of the non-lesioned striatum were found. Grafts placed in the non-lesioned striatum did not significantly change both rotational behaviour or [3H]DA uptake. The results show that unilateral fetal mesencephalic grafts producing behavioural improvement in the unilateral 6-OHDA lesioned rat induce changes in dopaminergic structures in the non-lesioned striatum.