[APUD system and neuroendocrine tumors ("apudomas")]

Current concepts of the APUD-system combining neuroendocrinal cells located in different organs are presented. The main feature of these cells is the capacity to accumulate precursors of biogenic amines, to decarboxylate them and to produce biogenic amines or polypeptide hormones. The problem of the development of tumours of these cells is discussed, and their morphological, histochemical and clinical features are described.