Glycerol administered orally in amounts of 25 to 50 gm four times daily in place of isocaloric amounts of dextrose during partial insulin withdrawal to four ketosis-prone diabetic patients decreased the concentrations of ketone bodies in blood and alveolar air to within normal limits in all patients. The daily glycosuria in these patients and in the additional three diabetic patients who failed to develop ketosis after partial insulin withdrawal decreased by an average of 85 gm/day when glycerol was substituted isocalorically for dextrose. This suggested that glycerol is a carbohydrate which can be metabolized without requiring insulin. No consistent effect on fasting total serum lipids, free fatty acids (FFA), and hyper-pre-beta-lipoproteinemia was demonstrable under the conditions of the experiment. The disappearance of serum-pre-beta-lipoproteins after several days of a high-carbohydrate, hypo-caloric diet in one patient was sustained during glycerol administration.