SUMMARY A protein capable of binding neurohypophysial hormones has been isolated from cod pituitary glands using gel filtration and ion-exchange chromatography. The cod protein which was acidic and rich in cystine had an amino acid composition closely related to those of the mammalian neurophysins. It had a maximum binding capacity of 2·2 μmole/14mg. for oxytocin, 2·1 μmole/14 mg. for [8-arginine]-oxytocin and 1·1 μmole/14 mg. for [8-arginine]-vasopressin. Thus the cod protein had a greater capacity for the endogenous pressor-antidiuretic peptide than for the analogous mammalian hormone.