1. The effects of a 48 h infusion of arginine vasopressin (AVP) were measured in five separate studies on four normal salt-restricted physicians, in whom fluid retention was prevented.
2. The infusion was associated with an increase in renal sodium excretion which continued during the 24 h after the infusion had been discontinuted.
3. During the infusion plasma renin activity (PRA), plasma aldosterone and noradrenaline, and packed cell volume (PCV) fell; glomerular filtration rate, assessed by endogenous creatinine clearance, increased.
4. The findings are best explained by a vasopressin-induced increase in plasma volume, which in the absence of fluid retention is likely to have been due to a redistribution of body water.