Three radiolabelled substances, 111In-pentetreotide, 99mTc-(V)DMSA and 123I-MIBG with different kinetics but similar tumor seeking behavior, were i.v. injected to assess and correlate their clinical value in metastatic malignant pheochromocytomas (4 patients), stage III and IV neuroblastomas (7 patients) and medullary thyroid carcinomas (6 patients). All II pheochromocytoma/neuroblastoma patients received i.v. a dose of III MBq (3 mCi) of 123I-MIBG and 185 MBq (5 mCi) of 111In-pentetreotide, within approximately weeks each other. Furthermore, in 4 of these patients as well as in all medullary thyroid carcinoma patients 111 MBq (3 mCi) of 99mTc-(V)DMSA were applied i.v. I week prior to the pentetreotide/mlBG scans. Four patients (malignant pheochromocytoma) with a total of 7 foci showing MIBG accumulation had 3 sites with pentetreotide and 1 site with (V)DMSA uptake, while in 7 patients (neuroblastora) with 15 foci showing MIBG accumulation 10 sites had detectable pentetreotide and 3 sites detectable (V)DMSA. Of the three radiotracers, 111In-pentetreotide used for somatostatin receptor identification holds promise mainly in cases where foci imaged with 123I-MIBG are negative. 111In-pentetreotide is unlikely to replace 123I-MIBG as a first-line routine diagnostic scintigraphic modality; compared to pentetreotide or MIBG, (V)DMSA seems to be highly sensitive only in medullary thyroid carcinomas.