Extracts of feline and human antropyloric mucosa contain two ACTH immunoreactive components. The main molecular component is radioimmunochemically and gel chromatographically indistinguishable from pituitary ACTH (1-39). Upon chromatography at two different pH, the main component and ACTH (1-39) displays identical changes in elution behaviour. In addition, antropyloric extracts contain a minor ACTH immunoreactive component, eluting in the void volume on Sephadex G-50 columns. The nature of this component is still undecided, but circumstantial evidence suggest that it may represent a biosynthetic precursor to the main ACTH-like component. © 1979.