Cells of carcinoid tumors which arise in the glandular stomach of old male and female Praomys (Mastomys) natalensis contain argyrophil granules when tissues fixed in formalin are colored with solutions of silver salts. The carcinoids metastasize in about 25 percent of cases, and are transplantable to other Mastomys. Tumor-bearing animals may show gastric and duodenal ulcers and multiple endocrine adenomas.