Abstract The physiologic changes during development of steroid-induced diuresis were examined in nephrotic children to determine the relationship between urinary aldosterone excretion and other responses. The earliest alterations occurred before diuresis and consisted of progressive decrements in urinary excretion of protein and aldosterone. In contrast, levels of serum albumin and of serum colloid osmotic pressure were not significantly altered until diuresis had begun. Plasma volume measurements, performed in a limited number of subjects, did not change consistently. The data are consistent with the interpretation that changes in aldosterone excretion during diuresis in the nephrotic syndrome are independent of serum albumin levels and, perhaps, of total circulating albumin. The findings suggest that excretion of edema fluid in this disease may be more significantly related to declining levels of aldosterone than to changes in serum albumin concentrations, serum colloid osmotic pressure, or total circulating albumin.