Urinary dopamine (DA) and sodium excretion in patients with nephrotic syndrome (NS) were studied under various sodium loading in metabolic ward. Twenty patients and 10 age-matched normal volunteers were enrolled in this study. When they were on a low-salt diet (34 mmol/d), urinary excretion of DA and sodium in patients with heavy edema were much lower than that in normal controls, while in patients with mild or without edema, urine DA and sodium excretion did not decrease significantly, but were not mobilized on sodium loading (170 mmol/d), and the plasma renin activity and aldosterone were not completely suppressed as well. The decrement of urine DA excretion was independent of Ccr or the severity of renal tubule lesions, but was associated with the severity of proteinuria. When the proteinuria reduced, urine DA and sodium excretion increased. From the above observations, we might assume that the abnormal retention of sodium and water in NS was due partly to a failure to mobilize DA in the kidney and the change of the physical environment in renal tubule caused by heavy proteinuria was responsible for it.