The therapeutic effects of prednisone and hydrocortisone were studied in 20 patients who had the complete idiopathic nephrotic syndrome characterized by proteinuria, edema, hypoproteinemia, and hypercholesteremia. Three patients with proteinuria but only minimal hypoalbuminemia, hyperlipoidemia, and edema were also included. The most sensitive and satisfactory criterion for judging the day-to-day status of these patients and for recognizing remissions and exacerbations was the 24-hour output of urinary protein. No evidence of benefit was seen when the dosage of prednisone was insufficient to decrease the proteinuria. When the dosage was sufficient (generally 40 mg. of prednisone or 160 mg. of hydrocortisone daily), a decrease in proteinuria occurred in the majority of patients. This was usually manifest within 10 days, and after a month of treatment the dosage was gradually reduced. One to three years after the steroid therapy, 12 of the 20 typical patients are well, 4 are improved, and 4 are unimproved or dead. The treatment was ineffective in the three atypical patients without hypoalbuminemia and hyperlipoidemia and in one patient in whom the nephrotic syndrome was caused by renal amyloidosis.