In rats with a lesion of the dopaminergic nigrostriatal pathway induced by 6-hydroxydopamine (6-OHDA), the histologic and functional viability of the striatal implant of fetal mesencephalic substantia nigra has been demonstrated. In the same model, the implant of adrenal medulla is also effective but less lasting. In monkeys with parkinsonism induced by MPTP there are suggestions of effectiveness of the fetal mesencephalic implant and also of other tissues such as placenta and sympathetic ganglion or sural nerve. Now the possibility of a better functional recovery by acting on the neuronal growth factors is being evaluated. In patients with Parkinson's disease, the accumulated experience indicates that 32% are improved with adrenal medulla implant, but the best candidates are those who also benefit from the available drug therapy without the risks of surgery. The implant of fetal tissue has been carried out in about 90 patients, with very variable results. In the most thoroughly investigated patients the improvement has been moderate. The future research points to the identification of the factors that control and regulate striatal reinnervation and the use of genetically determined cells. That would permit a more precise reposition of the biochemical deficiency in Parkinson's disease, without the ethical and practical problems derived from the use of fetal tissue.