UNLABELLED The somatostatin analog 111In-pentetreotide was evaluated in 11 children with sympathetic embryonic cell-derived tumors. METHODS Six neuroblastomas, four ganglioneuroblastomas and one ganglioneuroma (benign) were imaged 4 and 24 hr after injection of 111In-pentetreotide (5 MBq/kg) and 24 hr after administration of 123I-metaiodobenzylguanidine (MIBG) (3.7 MBq/kg). RESULTS Primary tumor was detected with both tracers in four of the five patients studied before surgery (one Stage III neuroblastoma, one Stage IV neuroblastoma, one Stage IVs neuroblastoma, one ganglioneuroblastoma), but the ganglioneuroma was not localized. Detection of bone marrow metastases was clearly better with 111In-pentetreotide in two patients, similar or slightly better with MIBG in six and (true) negative with both procedures in three. The positivity rate of 111In-pentetreotide for imaging of metastases was higher in undifferentiated malignant tumors (six neuroblastomas: two very positive, three positive, one true-negative) than in histologically well-differentiated tumors (four ganglioneuroblastomas: three weakly positive, one true-negative). All patients with positive 111In-pentetreotide imaging results had elevated urinary catecholamine levels, and the two most 111In-pentetreotide-positive metastases were found in neuroblastomas from children with an aneuploid primary tumor. The 111In-pentetreotide and MIBG results were only partly correlated with bone marrow status, as assessed by immunocytological and histological studies at the time of scanning. CONCLUSION Abnormalities detected in 111In-pentetreotide uptake were slightly different from those seen with MIBG as a first-line routine method in neuroblast-derived tumors. However, some MIBG as a first-line routine method in neuroblast-derived tumors. However, some MIBG-negative tumor sites were detected by 111In-pentetreotide in patients with neuroblastomas. Thus, 111In-pentetreotide could provide novel information on the biology and prognosis of tumors whose clinical significance remains to be defined.