From 1984 to 1989, 47 children with relapsed, refractory, and/or metastasized neuroblastoma were treated with 131I-metaiodobenzylguanidine (mIBG) in several different treatment combinations. At initial diagnosis, 36 children had Evans stage IV and 11 stage III disease. In 16 of the 47 children, tumor recurred after complete remission prior to mIBG treatment, 26 of 47 progressed from residual or nonresponding tumor, and in 5 of 47 tumor progression during chemotherapy was observed. Altogether the children were treated with a total of 112 courses (range 1-6) with a mean dosage of 8.9 +/- 6.7 mCi/kg body weight/treatment course. Total dose was 283.2 +/- 203.7 mCi for stage III and 388.9 +/- 218.6 mCi for stage IV. Nine of 47 children reached a complete or a very good partial remission (CR and VGPR) from mIBG treatment alone, 13 of 47 achieved partial remission (PR). In an early analysis, 10 patients treated with mIBG in the neuroblastoma trial NB 85 of the German Society of Pediatric Oncology showed no significant difference in survival time compared with 30 conventionally treated children. However, the recent therapy series has been done with higher doses of mIBG, and during improved therapeutic scanning many more bone lesions could be detected than during earlier diagnostic scanning. We conclude that mIBG treatment has not yet fulfilled the expectations for it but still seems for certain indications to be a promising tool to treat neuroblastoma in the future. Moreover, the frontier of neuroblastoma detection is still advancing.