The purpose of this work was to compare technetium-99m-diphosphono-propanedicarboxylate (DPD) and iodine-123-metaiodobenzylguanidine (MIBG) scans in the diagnosis and follow-up of neuroblastoma, and to study the role of histological differentiation in the uptake of MIBG. The uptake of MIBG and of DPD were studied retrospectively in 27 patients with neuroblastoma (primary, residual and recurrent tumours as well as bone and bone marrow metastases). The findings were related to the histological classification of the tumours as neuroblastoma (N1), differentiating neuroblastoma (N2) or ganglioneuroblastoma (N3). Uptake of MIBG by the primary tumour occurred in 17 of 19 patients, either at diagnosis or during follow-up. There were only two false-negatives with MIBG, both of which were N3. Ten patients were studied preoperatively with both MIBG and DPD. The primary tumour showed MIBG uptake in nine of the ten and DPD uptake in eight of them. Thirty-five sites of cortical bone metastasis were shown in eight patients by both MIBG and DPD, 12 sites in seven patients by MIBG only and seven sites in five patients by DPD only. In 14 patients both MIBG and bone scan were negative. Overall, MIBG demonstrated more lesions than DPD. Retrospectively several hot spots seen only with the bone scan are to be considered as false-positive. The highest incidence of false-negative MIBG and bone scans was observed in ganglioneuroblastoma with a predominance of the more mature component (ganglioneuroma).