The observed response to 131I-metaiodobenzylguanidine (MIBG) therapy in advanced neuroblastoma after conventional therapy, the non-invasiveness of the procedure, and the high metabolic activity which is frequently observed in untreated tumours led to the concept of substituting 131I-MIBG therapy for combination chemotherapy at diagnosis prior to surgery in patients with advanced disease/high-risk neuroblastoma. The objective of introducing 131I-MIBG therapy as the first therapy in the treatment schedule is to reduce the tumour volume, enabling adequate (> 95%) surgical resection of the tumour and to avoid toxicity and the induction of early drug resistance. The advantages of this approach are that the child's general condition is unaffected or improved before it undergoes surgical resection and that chemotherapy is reserved to treat minimal residual disease postoperatively. Thirty-one children who presented with inoperable neuroblastoma (10 Evans stage III, 21 stage IV) were treated according to this protocol. The objective response to the 131I-MIBG therapy at diagnosis with respect to the volume of the primary tumour, the metastases and catecholamine excretion in urine varied from 72 to 81%, which is better than after conventional treatment. Nineteen of 27 evaluable patients (70%) had complete or > 95% resection of the primary tumour or did not require surgery at all. Only 11 of 31 patients developed isolated thrombocytopenia and, despite the fact that the bone marrow was invaded in 16 patients, moderate bone marrow depression occurred in only two cases.(ABSTRACT TRUNCATED AT 250 WORDS)