Between 1989 and 1990 nine children with neuroblastoma stage IV (according to Evans) have been treated with high-dose [131I-meta]Iodobenzylguanidine (HD-mIBG). The total HD-mIBG dose administered to each child was at mean 699.3 +/- 111 MBq/kg body weight. Prior to (median 28 days) and after (median 50 days) HD-mIBG treatment a diagnostic scan with [123I-meta]Iodobenzylguanidine ([123I-m]IBG) was performed. Scans performed with HD-mIBG were superior to diagnostic scans for the detection of bone lesions in 8/9 children, for the detection of soft tissue lesions in 4/9 children, and for a more precise diagnosis of the primary tumor in 1 child. In 4 children lesions which were primarily identified in the therapeutic scan could be further observed in posttherapeutical examinations.