Acute changes in adrenocortical function were assessed by a method which permits simultaneous determination of cortisol and short-term cortisol secretion rates from specific activities in serum. Four children were studied during the first two hours of their initial hospitalization for impending ketoacidosis. Three were acidotic (plasma bicarbonate [unk] 19 mEq/liter); two of these were restudied one week later following stabilization of their disease. In all six studies cortisol secretion rate was directly correlated to the degree of acidosis (r =.96), being high in the presence of, but normal in the absence or following correction of, acidosis. These studies document the magnitude of adrenal response to the stress of diabetic ketoacidosis. The consistent presence of normal cortisol secretion rate in diabetic children without acidosis argues against the contention that increased cortisol secretion is a factor in the pathogenesis of juvenile diabetes mellitus.