The cDNA encoding the 29 amino acid-long neuropeptide galanin and its flanking peptide galanin message associated peptide (GMAP), has been cloned and sequenced from mouse hypothalamic cDNA. The primary sequence of mouse galanin is GWTLNSAGYLLGPHAIDNHRSFSDKHGLT, followed by an amidation signal GKR. There are now 12 galanin sequences known: human, porcine, dog, rat, bovine, chicken, sheep, alligator, bowfin, dogfish, trout and mouse. The N-terminal 14 amino acids are identical in all of these species and the whole primary sequence of mouse galanin is identical to that of rate galanin. The mouse C-terminal flanking peptide, the GMAP, which is encoded on the same mRNA as galanin, shows a high degree of homology with all other known GMAP sequences but is not identical to any of them and it is more charged than the other GMAP sequences. Synthetic mouse galanin was found to displace [125I]mono-iodo-Tyr26 galanin (porcine) from receptors in the mouse hypothalamic membranes with high affinity (KD = 0.9 nM). Estrogen treatment of mice (0.1 mg/kg i.p.) for 6 h, which elevates the rat pituitary galanin mRNA levels, does not affect the galanin mRNA levels in mouse hypothalamus and pituitary. Neither does a subchronic glucocorticoid treatment (dexamethasone, 0.5 mg/kg i.p. for 7 days) affect these mRNA levels.