The role of radiolabeled meta-iodobenzyl-guanidine (mIBG) is established in the detection and the staging of neuroblastoma. We designed a study of mIBG scanning for patients with Ewing's sarcoma, a tumor for which a neuroectodermic origin has been proposed. We explored 15 children with round cell sarcoma of bone by a whole body scan carried out 24 hours after injection of 123-I mIBG. No patient demonstrated significant uptake either at the site of the primary or at the sites of metastases. These results suggest that despite its neural histogenesis Ewing's sarcoma is a member of the nonneuroblastoma neural crest tumors, which does not produce or store adrenergic metabolites.