Three cases of idiopathic edema are reported with the results of water loading tests. Free water clearance and fractional sodium excretion revealed that three cases were different in water and sodium retention both in supine and upright positions. Aldosterone, plasma renin activity and antidiuretic hormone seemed to little to correspond to water and sodium retention; whereas atrial natriuretic peptide markedly increased in the upright position in all the cases. These data suggest that three cases cannot be explained by a single factor, but that enhanced reduction of venous return to the heart in the upright position may be a common feature in all three cases.