Apudomas are neoplasms known to produce many biologically active amines. Some of these tumors have been known for 70 years, but over the last 15 years a wealth of new knowledge has been obtained. This study reports experience with apudomas over an 8-year period (1975-1983) at The Piedmont Hospital. There were 159 tumors with the potential for producing various ectopic hormones as well as biologically active amines, including 112 oat cell carcinomas, 37 carcinoid tumors, 4 paragangliomas, 2 pancreatic islet cell tumors, 2 medullary thyroid carcinomas, 1 pituitary adenoma, and 1 pinealocytoma. Of the 112 oat cell carcinomas, only 2 per cent had hormone-related symptoms. Of the carcinoid tumors, 12 were found in the appendix, 9 in the small intestine, 9 in the lungs, 4 in the colon and 2 in the rectum. Nineteen of the 37 carcinoids had hormone-related symptoms but none had a classic carcinoid syndrome. A third group of apudomas included several of relative rarity, the paragangliomas, the medullary thyroid carcinomas, the pancreatic islet cell tumors, pituitary adenomas, and pinealocytomas. Of this latter group, only the pancreatic islet cell tumors had symptomatology that could be related to ectopic hormone production.