Chicken posterior pituitary tissue was partially fractionated by extraction with 0.1 M HC1 followed by gel exclusion chromatography. Two fractions, B and C, bound oxytocin. Two components of fraction B and at least 1 component of fraction C had properties characteristic of mammalian neurophysins: they appeared to be synthesized in the hypothalamus, were depleted upon osmotic stress, were rich in residues of cysteine and the 2 components of B bound to [8-lysinel]-vasopressin coupled to Sepharose.