Adrenal medullary catecholamines were measured in tissue samples from eight patients who underwent autologous transplantation of the adrenal medulla to the caudate nucleus as a treatment for Parkinson's disease. These adrenal catecholamine levels were compared to a group of patients of similar age who underwent unilateral nephrectomy for renal cell carcinoma. The levels of each catecholamine, expressed as nanomoles per milligram wet weight tissue, were significantly lower (P less than or equal to 0.005) in the parkinsonian patients than in the nephrectomy patients. These observations support data reported previously from autopsy specimens and suggest that the adrenal medullae of parkinsonian patients may be a compromised source of dopamine-producing tissue; this may limit its effectiveness in eliciting maximum clinical improvement following transplantation.