Twenty-four-hour urine kallikrein excretion (Uka), urine protein excretion, renal sodium handling, and the activity of the renin-angiotensin-aldosterone system were serially studied in 11 children at three different stages of the minimal change nephrotic syndrome (MCNS)-edema forming state, proteinuric steady state in which a relapse of the disease was just starting but no edema as yet and remission. The value for Uka was significantly increased in the edema forming state in contrast to the normal values of proteinuric steady state and remission. Serum sodium concentration was only decreased in the edema forming state and the degree of hypoalbuminemia and proteinuria did not differ between the edema forming and proteinuric steady states. Urine volume, absolute and fractional sodium excretion were significantly decreased in the edema forming and proteinuric steady states as compared with those in remission, suggesting that sodium retention was present in both states of the disease although the change in these parameters was more profound in the edema forming state than in the proteinuric steady state. Creatinine clearance did not differ among each stage of the disease. Plasma renin activity and plasma aldosterone concentration were significantly increased in the edema forming state as compared with those in the proteinuric steady state and remission. Plasma renin activity and plasma aldosterone concentration were significantly correlated directly with Uka and plasma aldosterone concentration was correlated inversely with urine sodium excretion. No relation was noted between Uka and other variables.(ABSTRACT TRUNCATED AT 250 WORDS)