Ten patients with advanced Parkinson's disease, presenting with tremor, rigidity and akinesia had autologous adrenal medullary transplantation taken from the left adrenal gland to the head of the right caudate nucleus. Particular attention was taken to avoid prolonged exposure of the adrenal tissue before transplantation and to separate the medullary from the cortical adrenal tissues. Postoperative CT scans confirmed the correct position of the transplants. Differences between pre- and 1-year postoperative clinical conditions were statistically evaluated, with patients under medical (L-dopa) treatment and after the medication was temporarily discontinued. Performance of motor tasks was tested to differentiate slowness of movements imposed by excessive muscular tension (rigidity) from that secondary to delayed reaction time to sensory demands (akinesia). Two deaths occurred 35 and 69 day after surgery for causes not related to the surgical procedures. One of those patients had remained stable neurologically and the other had deteriorated to progressive dementia and catatonia. At autopsy, no lesions in the CNS other than those expected from the surgical procedure were evident, and histological examination failed to reveal chromaffin cells in the head of the right caudate nucleus. Evaluation of the 8 cases that survived for 1 year revealed no significant improvement in their clinical or motor task performance, when considered as a group. However, cases with mild akinesia did better than cases with moderate to advanced akinesia, suggesting that transplantation is indicated in cases with rigidity, but not in cases with 'negative' symptoms of Parkinson's disease. All cases required postoperative medication.