Fetal conditionally immortalized striatal cells ST14A and human mesencephalic neural progenitor cells (NPCs) were studied with respect to proliferation and differentiation in in vitro experiments. In in vivo experiments, human NPCs were investigated after transplantation into neonatal and adult hemiparkinsonian rat striatum. The survival, migration and dopaminergic (DAergic) differentiation of human NPCs in the host brain was investigated. Improvement in lesion-induced motor impairment has been demonstrated in both groups of hemiparkinsonian rats, independently from DA-ergic differentiation.