We report heretofore undescribed clinical and histological features of a patient with idiopathic Parkinson's disease who showed marked and persistent motoric benefit from an adrenal medulla autograft for 18 months following grafting. The patient returned to the preoperative level of disability prior to his death 30 months after implantation, the longest survival to date for an adrenal transplant. The graft site was primarily necrotic and large numbers of macrophages were still present at the time of death. A few tyrosine hydroxylase-immunoreactive cells were found within the graft, providing the first evidence that adrenal medullary cells may be viable and produce catecholamines following human transplantation, A dense network of tyrosine hydroxylase-immunoreactive terminals and processes was also seen ventral to the implant site and on both of its lateral borders. This response may represent sprouting by residual host dopaminergic neurons mediated by the vigorous response to injury displayed by the host striatum The relative paucity of surviving chromaffin cells, however, provides further evidence that adrenal medulla grafts survive poorly following intracerebral implantation, and factors other than dopamine replacement may be responsible for most of the functional effects observed following chromaffin cell transplantation.