The value of the subunits of human chorionic gonadotropin (hCG) as tumor markers is controversial. The production of hCG-alpha and hCG-beta by 214 nontrophoblastic exocrine and by 416 endocrine tumors was analyzed by using immunocytochemical technics. hCG-alpha immunoreactivity was found in 131 of 416 endocrine and in 8 of 214 nonendocrine tumors. hCG-beta could not be visualized specifically with the use of two polyclonal antisera and one monoclonal antibody. The authors conclude that (1) hCG-alpha is neither a tissue nor a tumor-specific marker; (2) hCG-alpha is produced by a variable proportion (21-55%) of endocrine tumors arising in various organs but not by ileal carcinoids, paragangliomas, pheochromocytomas, nor Merkel cell tumors; (3) hCG-alpha is a marker of malignancy only in pancreatic endocrine tumors; and (4) hCG-beta is rarely, if ever, produced by tumors.