Hormonal balance was studied in eight insulin-treated diabetic children who had excessive glycosuria. Glucose, growth hormone, and cortisol in plasma were determined every 0.5 hr for 48 hr. Total catecholamines and glucose were measured and tests for ketones done in 2-hourly collections of urine. Intermittent hypoglycemia as low as 20 mg/100 ml and swings of the blood sugar curve by 200-300 mg/100 ml within 2-4 hr were documented in most patients. Peaks of growth hormone concentration in plasma (8-78 ng/ml) followed almost every sharp fall in blood glucose; these peaks were usually followed by abrupt rises of glucose and prolonged hyperglycemia. Cortisol concentration was usually within the high normal range; there was no consistent relationship to the concentration of glucose. Urinary excretion of catecholamines in most patients was between 1 and 6 mug/hr; three patients excreted up to 8-23 mug/hr during short periods and up to 190 mug in 24 hr. The causes for the high excretion of catecholamines are unknown and may not have included hypoglycemia.