Open autologous adrenal medullary to caudate nucleus transplantation was performed in 12 patients with advanced Parkinson's disease (PD). Ten of these patients had diurnal response fluctuations including "wearing off" and "on/off" phenomena. All of the patients were no longer satisfactorily responding to levodopa/carbidopa and dopamine agonists. The mean age of the patients was 55.1 years (range 37-65 yrs); mean duration of PD was 11.7 years (range 4-40 yrs); mean stage "on" was 3.3 (range 2-4); mean stage "off" was 4.8 (range 4-5). Mean duration of follow up from surgery was 10.4 months (range 2-17 months). Three patients improved dramatically with major changes in their lifestyle. The course of improvement in these 3 patients was different in each, implying that different mechanisms were responsible for the improvement. One of the patients died unexpectedly. In this patient, there were no surviving adrenal cells. Three patients improved moderately. Patients reported that they were "on" longer and had to take medication less often and were less dependent on individual doses of levodopa/carbidopa. The improvement has been sustained in two patients. However, in one of these patients there had to be frequent changes in scheduling to maintain the improvement. Two patients after technically successful implants did not improve. One of these patients subsequently died. In this patient there were a few surviving adrenal medullary cells. Four patients suffered major complications. One patient had a cerebral infarction and two had cerebral hemorrhages. One of these patients has shown a good recovery. One patient with autonomic insufficiency had a cardiac arrest with cerebral anoxia one week after surgery. This patient has shown a partial recovery.(ABSTRACT TRUNCATED AT 250 WORDS)