The renin-angiotensin-aldosterone system was evaluated in two types of uncontrolled diabetes: a) diabetic ketoacidosis, and b) nonketotic hyperglycemia. In thirteen patients with ketoacidosis, mean plasma renin activity (PRA) was 58 ± 12 (S.E.M.) ng. per milliliter per hour and in four patients, plasma aldosterone was 82 ± 17 ng. per 100 ml. Corresponding values for upright saltdepleted subjects were 13 ± 2 and 62 ± 8. In eleven diabetics with nonketotic hyperglycemia (mean glucose 318 ± 19 mg. per cent), mean blood volume was 4,660 ml. and PRA 2.1 ± .7. After control of the diabetes (mean glucose 129 ± 13) blood volume was 4,553 ml. and PRA 3.3 ± 1 (N.S.). The results suggest that: 1) diabetic ketoacidosis is a state of severe secondary aldosteronism, 2) no significant change in blood volume or PRA occurs during short periods of hyperglycemia, and 3) insulin is not necessary for renin release.