1. Due to their common origin from the neural crest the hormonogenic cells of the intestinal tract show similar cyto-chemical and ultra-structural characteristics. 2. Hyperplasiae and tumors of these cells lead to excessive hormone production with its consequences on the reacting organs. 3. Hormone producing tumors can be confined to one organ only, but as multiple endocrine adenomatosis they can afflict several organs. 4. Diagnosis of most hormone producing tumors is possible with the adequate radio-immunologic tests. Radiologic and endoscopic examinations can contribute to the localization of the tumor. 5. Surgical resection of the tumor or of the reacting organs impaired by the overproduction of hormones from the tumor is the indicated therapy. Medicamentous therapy is rarely successful. 6. The growth of most hormonogenic tumors is relatively slow. Rates of survival of up to 30 years have been known, even after formation of metastases of the tumor. Effects of hormone overproduction on other organs can reduce the prognosis.