The potential role [131I]MIBG therapy in untreated, inoperable cases of neuroblastoma (NB) in children was evaluated. Six children, aged 10 months-5 years, were treated at diagnosis. Five (4 stage III and 1 stage IV NB) underwent [131I]MIBG treatment alone (single doses ranging from 2.9 to 6.1 GBq of high specific activity [131I]MIBG. In one case (stage IV NB) [131I]MIBG was preceded by Cisplatin administration (20 mg/m2/day) given over a 5 day period. The results obtained in the first 5 cases were as follows: 1 complete response still lasting after 5 years; 1 partial and 1 minor response allowing further surgery and chemotherapy; 2 stabilization of the disease. The treatment was well tolerated with minimal toxicity. However, apart from the first case all these children relapsed and subsequently died. Therefore [131I]MIBG therapy (9.1 GBq given in 2 courses) combined with Cisplatin as a "radiosensitizer" was used in the sixth case, a patient with widespread bone metastases and massive bone marrow involvement. A very good partial response was obtained in this case. Further surgery (of the primary NB) and multidrug chemotherapy was then possible. In conclusion, [131I]MIBG therapy at diagnosis appears to be effective, low toxic treatment of NB; when integrated with Cisplatin its efficacy seems to improve even more.