The primary structure of frog neurotensin (fNT) has recently been determined and it has been shown that fNT is a potent stimulator of -MSH secretion by frog pituitary melanotropes. Frog neurotensin is a potent stimulator of the electrical activity of frog pituitary melanotropes, and the electrophysiological response evoked by frog neurotensin can be accounted for by activation of a G(q/11)-protein-coupled receptor subtype whose pharmacological profile shares similarities with those of mammalian NTS1 and nts2 receptors.