Our experience in scintigraphic diagnosis using 123I/131I-metaiodobenzylguanidine (MIBG) on 37 children with neuroblastomas stage III-IV is reported and discussed, together with the results obtained by other authors on MIBG diagnosis at the International Workshop of Pediatric Oncology held in Rome in September 1986. In our own investigation, 49 examinations were undertaken with 123I-MIBG and 66 with 131I-MIBG partly under therapy conditions with high-activity doses of 131I-MIBG. There were 29 neuroblastomas, 3 ganglioneuromas, and 3 ganglioneuroblastomas. The localization of all primary tumors was over 90%; for neuroblastomas with a high level of catecholamine excretion, over 95%. The specificity was about 100%. The sensitivity with respect to tumor relapse and all localization of metastasis and bone-marrow tumor infiltration in the follow-up-phase approaches was 70% during or after therapy. What emerges from the experience of most investigators is that 123I-MIBG is the agent best suited to detect tumor relapse and metastasis, especially in the bone marrow. MIBG examinations are of great value in follow-up studies for detecting tumor relapse and bone marrow infiltrations, especially before the onset of clinical symptoms and other indications.