The endocrine cells of the starfish digestive tract are spindle-shaped, contacting both the lumen and the basiepithelial plexus. Silver impregnation labels the basiepithelial and subcoelomic plexuses as well as these cells. Twenty antisera have been tested using the avidinbiotin method, in order to identify the regulatory substances involved in this system. Endocrine cells and nerves immunoreactive to GFNSALMFamide- ($1), FMRFamide-, peptide tyrosine-tyrosine- (PYY), pancreatic polypeptide- (PP), melanocyte stimulating hormone-(eMSH) and peptidylglycine alpha-amidating monooxygenase- (PAM) specific antisera have been found in the epithelium. The antibodies against SI, a peptide isolated from the nervous system of a starfish, and c~MSH, stain both the basiepithelial plexus and the subcoelomic plexus, but the others react only with nerves in the basiepithelial plexus. Absorption controls show that antibodies for $1 and FMRFamide totally crossreact recognizing the same molecule, possibly $1. The other antibodies do not show cross-reactivity to any of the rest, and thus we conclude that these regulatory peptides are present in starfish. This is the first report of the presence of FMRFamide, PYY, eMSH and PAM in the Echinodermata. Under the electron microscope the endocrine cells exhibit secretory granules, microtubules and mitochondria. Direct contact with the subcoelomic plexus can be observed.