Galanin message-associated polypeptide (GMAP) is processed from preprogalanin. Recently, GMAP-like immunoreactivity was demonstrated in insulin cells in the endocrine pancreas. We therefore examined whether synthetic rat GMAP, like galanin, inhibits glucose-stimulated insulin secretion from isolated rat and mouse islets. We found, however, that over a wide dose range (0.1 nM to 1 microM) GMAP did not affect insulin secretion stimulated by 8.3 or 11.1 mM glucose during a 60-min incubation of single rat or mouse islets. In contrast, rat galanin, as expected, completely abolished glucose-stimulated insulin secretion at 100 nM. Thus, in contrast to galanin, GMAP does not affect insulin secretion in isolated rodent islets.