The significance of ketosis in this syndrome has been evaluated from several viewpoints. With respect to acid-base considerations (pH, anion gap), ketosis was not very significant. However, with respect to sustained hyperglycemia, the combustion of less glucose than normal by the brain is critical and it is likely that ketone body metabolism plays an important role in this regard. This point can be underscored by a quantitative example. First, assume that the maximum rate of new glucose production in a fasted subject is less than 100 g of glucose per day. Second, since the brain will burn 100 g of glucose per day in a non-ketotic subject, it follows that, even in the absence of glucosuria, there will be a net daily consumption of glucose. Since the hyperglycemic individual has only an extra 100 or so g of glucose, it follows that the blood glucose concentration would approach the renal threshold in several days in the absence of ketosis. Recall that this is a minimum estimate because glucose oxidation in other organs and glucosuria will remove an additional quantity of glucose. Hyperglycemia can only be maintained in the absence of glucose intake if there is a reduced rate of glucose metabolism in the brain. The brain can diminish its rate of glucose catabolism by several mechanisms, including a diminished metabolic rate in the brain and/or the consumption of non-glucose fuels (free fatty acids or beta-hydroxybutyrate) by this organ.(ABSTRACT TRUNCATED AT 250 WORDS)