[Yttrium-90-DOTA-Tyr(3)]-octreotide (DOTATOC) and [(177)Lu-DOTA-Tyr(3)-Thr(8)]-octreotide (DOTATATE) are used for peptide receptor-mediated radionuclide therapy (PRMRT) in neuroendocrine tumours. No human data comparing these two compounds are available so far. We used (111)In as a surrogate for (90)Y and (177)Lu and examined whether one of the (111)In-labelled peptides had a more favourable biodistribution in patients with neuroendocrine tumours. Special emphasis was given to kidney uptake and tumour-to-kidney ratio since kidney toxicity is usually the dose-limiting factor. Five patients with metastatic neuroendocrine tumours were injected with 222 MBq (111)In-DOTATOC and (111)In-DOTATATE within 2 weeks. Up to 48 h after injection, whole-body scans were performed and blood and urine samples were collected. The mean absorbed dose was calculated for tumours, kidney, liver, spleen and bone marrow. In all cases (111)In-DOTATATE showed a higher uptake (%IA) in kidney and liver. The amount of (111)In-DOTATOC excreted into the urine was significantly higher than for (111)In-DOTATATE. The mean absorbed dose to the red marrow was nearly identical. (111)In-DOTATOC showed a higher tumour-to-kidney absorbed dose ratio in seven of nine evaluated tumours. The variability of the tumour-to-kidney ratio was high and the significance level in favour of (111)In-DOTATOC was P=0.065. In five patients the pharmacokinetics of (111)In-DOTATOC and (111)In-DOTATATE was found to be comparable. The two peptides appear to be nearly equivalent for PRMRT in neuroendocrine tumours, with minor advantages for (111)In/(90)Y-DOTATOC; on this basis, we shall continue to use (90)Y-DOTATOC for PRMRT in patients with metastatic neuroendocrine tumours.