It is well established that ACTH and beta-lipotropin (LPH) originate from a common precursor molecule. Recently the complete complementary DNA sequence of the bovine precursor was reported, and within the cryptic sequence of this molecule is a third melanocyte stimulating hormone (MSH) region tentatively named gamma-MSH. The signal peptide of this molecule consists of 26 amino acids in both the rat and mouse. Pulse-chase experiments using both rat and mouse pituitary cells, showed the gradual maturation of this common precursor to proceed via the initial cleavage of the carboxy terminal beta-LPH, followed by release of ACTH, leaving an NH2-terminal extension of about 105 amino acids, which does not seem to undergo appreciably further maturation. It is within the sequence of this NH2-terminal extension that gamma-MSH is located. It is not yet clear what the biological role of this molecule is and whether gamma-MSH itself is released. Recently, it was shown that a synthetic 12 amino acid bovine gamma-MSH fragment possessed very little melanophore-stimulating activity as compared to alphs-MSH. We report here the successful purification of the human NH2 terminal cryptic peptide, its amino acid composition and present some of its tryptic fragments. The data show that human and bovine gamma-MSH have indentical amino acid composition.