1. The role of arginine-vasopressin in the pathogenesis of malignant deoxycorticosterone (DOC) hypertension of rats was investigated.
2. In rats with malignant DOC hypertension plasma arginine-vasopressin concentrations increased more than tenfold subsequent to volume depletion and a rise of serum osmolality.
3. The injection of a specific antibody serum for arginine-vasopressin caused a marked fall of blood pressure in rats with malignant DOC hypertension, whereas the injection of angiotensin II antiserum did not affect blood pressure.
4. In rats exhibiting a benign course of DOC hypertension plasma concentrations of arginine-vasopressin were increased threefold in comparison with normotensive control rats; the injection of an arginine-vasopressin antiserum induced a significant but small fall of blood pressure.
5. It is concluded that in the pathogenesis of malignant DOC hypertension arginine-vasopressin might play the role that the renin—angiotensin system plays in the pathogenesis of malignant renal hypertension.