Polyadenylated messenger RNA has been isolated from bovine adrenal medulla and anterior and neurointermediate pituitary gland as well as from human phaeochromocytoma. The mRNAs were translated in the presence of protease inhibitors in the rabbit reticulocyte cell-free system, containing [3H]leucine. The primary translation products were analyzed for chromogranin-like polypeptides by immunoprecipitation with chromogranin A antiserum and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The results show that each of the four mRNAs directed synthesis of a series of chromogranin-like proteins varying in apparent Mr between 25,000 and 120,000. The immunoreactive chromogranins coded by the three bovine mRNAs were of identical apparent Mr while the human chromogranins tended to be slightly larger. A chromogranin A-like polypeptide with apparent Mr = 72,000 was the main immunoprecipitable translation product of adrenal medulla mRNA, while that of anterior pituitary mRNA had a Mr = 87,000, that of neurointermediate pituitary mRNA a Mr = 30,000, and that of human tumor mRNA a Mr = 115,000. The results suggest that the differently sized chromogranins were coded by separate mRNAs and did not derive from a high molecular weight precursor by either nonspecific or specific post-translational protolysis.