The present report concerns the immunocytochemistry of various peptide hormones and in particular their location in nervous structures. However, since the hormones observed in the neuroadenohypophysis and the digestive tractus have been examined elsewhere, they have been excluded from this study, except when considered outside there precise areas. The immunocytology of the following neuropeptides is presented, especially the particular details related to their demonstration: 1) The hypothalamic hypophysiotropic factor: LH-RF, SRIF, TSH-RF; derivatives from the so-called proopiocortine found by Mains and Eipper (1977), namely beta-LPH, enkephalins, endorphins, alpha-MSH- and ACTH-like antigens; 2) Prolactin and somathormone found outside the pituitary; 3) Gastro-intestinal hormones and their location outside the digestive hormones and their location outside the digestive mucosa, namely VIP, CCK, substance P; 4) Angiotensin II in nervous structures; 5) Neurotensin; 6) Thyrocalcitonin; 7) Relaxin, and the problem of its presence in the adult male genital tract. New data in invertebrate located vertebrate neuropeptides-like antigens in the nervous structures of pro-chordates (Ascidians) insects, crustaceans, annelids. These last findings underline the extensive significance of such hormonal molecules previously considered to be specific for vertebrates.