Stereotactic adrenal medullary transplantation into the striatum was performed in 5 patients with severe Parkinson's disease. Four patients had previously been treated with thalamotomies and all were on L-dopa therapy with significant side effects. All 5 patients had shown marked disability before the procedure. Autologous adrenal medullary tissue was sliced into 20-30 fragments and transplanted into two sites of the caudate nucleus, one at the ventricular surface and the other in the head of the nucleus. The cases were followed for 4-5 years (mean 4.5 years), except for 1 patient who died of unrelated causes 22 months after the procedure. Initial bilateral symptom improvement was observed in all cases for 9-21 months (mean 15.2 months) after transplantation without L-dopa therapy. Later, these improvements progressively deteriorated. L-dopa therapy had to be resumed for all. MRI on the long-term follow-up showed the transplanted tissue as a low signal intensity area surrounded by high intensity spots in T1- and T2-weighted images. Compared to previous MR studies, the transplanted tissue was shrunken and presumed nonviable.