The plasma renin activity (PRA), plasma aldosterone level, and blood volume were studied in 12 patients with idiopathic nephrotic syndrome. As a whole, the patients with the nephrotic syndrome showed significant elevations of the PRA and plasma aldosterone but not in blood volume compared to the normal controls. Six patients who had a larger blood volume than the control group had decreased PRA, while the other 6 patients who had a smaller blood volume than the control group had an increased PRA. Also noted was that there was no histopathological difference of kidney diseases between the patients with increased blood volume and decreased blood volume. Though there was no correlation between serum albumin, PRA, and plasma aldosterone levels, there was a tendency of increased blood volume as serum albumin decreased.