Gut hormones immunoactivities were studied in the gut of grey mullet ( Mugil cephalus L. ) using ant isera against mammalian 5..hydroxytryptamine ( 5..HT) , somatostatin ( SST) , gastrin ( GAS) , P substance, vasoactive intestinal peptide ( VIP) , insulin and glucagon. 5..HT, SST, VIP, GAS, P substance immunoactive cells were detected in the gastroenteric muco sa of grey mullet, but the immunoactivity of glucagon and insulin in the gut mucosa was not detected. In the present paper, the morphological characteristics and the distribution density in all stomach intestinal segments of immunoreactive endocrine cells in the gastrointestinal tract were described. At the same time, the possible way of secretion and the physiological function of these endocrine cells were discussed.