Specific monoclonal and polyclonal antisera raised against the starfish SALMFamide peptides S1 and S2, have been used to determine the tissue distribution and cellular localization of these novel neuropeptides in the starfish Asterias rubens. The present study examines the digestive system of this animal using single- and double-labelling optical immunocytochemistry (ICC). The results reveal a widespread neuronal localization for S2 to axons and perikarya throughout the digestive system. Double-labelling revealed a predominantly separate localization for S1 and S2 immunoreactivity. This distribution, in conjunction with previous pharmacological studies implicate a role for this peptide in gut relaxation.