Abstract.An oral water load of 20 ml (kg body wt)‐1was given to seventeen patients with the nephrotic syndrome and fifteen healthy control subjects. Diuresis (D), free water clearance (CH2O), plasma concentrations of arginine vasopressin (AVP), angiotensin II (AII) and aldosterone (Aldo) were determined before and 3 times during the first 4 h after loading. In the nephrotic syndrome D was significantly lower 1–2 h after loading than in the control subjects, predominantly due to a lower CH2O(2·61 and 7·01 ml min‐1(medians),P<0·01).Creatinine clearance and the maximum increase in CH2Owere significantly correlated in patients with the nephrotic syndrome (ρ= 0·721,n= 17,P<0·01) and the control subjects (ρ= 0·596,n= 15,P<0·01). AVP was reduced in both groups during loading, but AVP was clearly elevated in the patients with the nephrotic syndrome when compared to the control subjects both before (3·0 and 1·9 pmol 1‐1,P<0·01) and during loading. There was a significantly negative correlation between CH2Oand AVP in both groups. AII and Aldo were reduced during loading, but the levels were the same in the patients and in the control group, and AII and Aldo were not correlated to CH2O. It is concluded that patients with the nephrotic syndrome excrete an oral water load more slowly than healthy control subjects, and that this phenomenon partly is due to reduced glomerular filtration rate and part