Parkinson's disease (PD) patients can suffer intolerable disability despite currently available therapies, and a treatment that slows disease progression and/or restores function is an urgent priority. Much attention has focused on transplantation strategies as a treatment option because of the potential of transplanted dopamine nerve cells to replace degenerating dopamine neurons. The first studies of transplantation in humans utilized autologous adrenomedullary cells implanted into the caudate nucleus. Variables that must be considered in developing a transplant protocol include method of tissue storage prior to surgery, donor age, number of donors implanted, site of transplantation, type of transplant, and the use of immunosuppression. To better define the safety and efficacy of fetal nigral transplantation as a treatment for PD, the National Institutes of Health in the USA supported two double-blind, placebo-controlled trials. Transplantation of fetal mesencephalic dopamine neurons was associated with a potentially disabling off-medication dyskinesia.