The gastrointestinal tract of three Percida, Lateolabrax japonicus, Epinephelus septemfasciatus and Mugil cephalus, was investigated immunocytochemically for the occurrence of somatostatin-. seotonin-, gastrin-, pancreatic polypeptide(PP)-, cholecystokinin-8(CCK-8)- and glucagon-immunoreactive cells. In Lateolabrax japonicus and Epinephelus septemfasciatus, five endorcrine cell types, such as somatostatin-, serotonin-, gastrin-, PP- and CCk-8-immunoreactive cells were demonstrated. In Mugil cephalus, however, six endocrine cell types, such as somatostatin-, serotnin-gastrin-, PP-, CCK-8- and glucagon-immunoreactive cells were detected. Somatostatin- and serotonin-immunoreactive cells were detected in the gastric mucosa of all species. Glucagon-immunoreactive cells were found only in the gastric mucoas of Mugil cephalus. In the pyloric caeca, PP-and CCK-8-immnuoreactive cells fo all species. gastrin-immunoreactive cells of Epinephelus septemfasciatus and Mugil cephalus, and serotonin-immunoreactive cells of Epinephelus septemfasciatus were demonstrated. In the intestinal mucosa of all species, gastrin-, PP- and CCK-8-immunoreactive cells were detected, and in the intestinal mucosa of Epinephelus septemfasciatus serotonin-immunoreactive cells were also detected. The frequency of these immunoreactive cells differs from each portion of the gastrointestinal tract of all species.