Since February 1990, 74 patients (116 studies) underwent scintigraphy with meta-[131I]iodobenzylguanidine ([131I]MIBG). Eighteen patients had pheochromocytomas, 2 paragangliomas, 2 malignant insulinomas, 1 carcinoid, 2 medullary thyroid carcinoma and 49 children had neuroblastomas. Scintigraphy was performed following a thyroid blockade, at 24 and 48 hours after i.v. injection of 0.5 mCi/1.7 m2 [131I]MIBG. Grade of heart intensity (GHI) uptake and the intensity of salivary gland visualization (SGI) were estimated semiquantitatively, according to the method of Nakajo et al. Sensitivity in the primary pheochromocytomas was 93.9%; sensitivity and specificity in the primary neuroblastomas were 93.7% and 100% respectively; in the secondary neuroblastomas they were 100%, and 100%. Metastases in 2 malignant insulinomas and in 1 case of medullary thyroid carcinoma were also demonstrated. Only one false negative (in pheochromocytoma) and one false positive (Conn's syndrome) result was obtained. Mean values and range of MIBG uptake measured according to Shulkin's procedure were: for pheochromocytoma 3.95% (0.1-15), primary neuroblastoma 0.7% (0.05-1.92%), and neuroblastoma metastases 0.12% (0.002-0.83%). Assessment of [131I]MIBG uptake seems to be helpful in the follow-up of some neural crest tumors and is essential as a prelude to [131I]MIBG therapy.