Various tumors of neuroendocrine origin that have amine precursor and decarboxylation (APUD) characteristics can be visualized in vivo after intravenous injection of the somatostatin analogue [123I-Tyr3]-octreotide. However, the relatively short effective half-life of this compound and the high background of radioactivity in the abdomen are drawbacks in its application. Therefore, an 111In-coupled somatostatin analogue ([111In-DTPA-D-Phe1]-octreotide) was developed. This analogue is excreted mainly via the kidneys, 90% of the dose being present in the urine 24 h after injection. Using 111In-octreotide scintigraphy, 7 out of 7 gastrinomas, 4 out of 7 insulinomas, 1 out of 1 glucagonoma, 3 out of 3 unclassified apudomas, but none out of 18 exocrine pancreatic carcinomas were visualized. Also, 19 out of 19 carcinoids, 15 out of 15 glomus tumors, 8 out of 12 medullary thyroid carcinomas, 6 out of 6 small cell lung carcinomas, 4 out of 4 growth hormone-producing and 6 out of 9 clinically nonfunctioning pituitary adenomas were visualized. Apart from APUD-cell-derived tumors, 111In-octreotide scintigraphy was also successfully applied to visualize breast cancer, lymphomas and granulomas. In 39 out of 50 patients with breast carcinoma, 10 out of 11 patients with non-Hodgkin lymphomas, 3 out of 3 patients with Hodgkin's disease, and 8 out of 8 patients with sarcoidosis, tumor sites accumulated radioactivity during octreotide scintigraphy. In a considerable number of patients with carcinoids and glomus tumors, but also in patients with granulomas and lymphomas, 111In-octreotide scintigraphy revealed more tumor sites than did conventional imaging techniques.(ABSTRACT TRUNCATED AT 250 WORDS)