In the literature of recent years many articles are to be found relating to acidosis, acetonuria, and acetonemia in children. These terms frequently are used synonymously, and many widely different conditions are described under these headings. In all reports of acetonemia that I have found various conditions are described in which the urine is characterized by the presence of acetone and diacetic acid. With the exception of Marriott's1 papers I have found no records of the determination of acetone bodies (beta-oxybutyric acid, aceto-acetic acid, and acetone) in the blood of living children. This work was undertaken to determine the amount of acetone bodies in the blood of normal children and of children in various pathologic conditions, especially those with evidence of acidosis, such as, increased pulmonary ventilation, decreased carbon dioxid tension of the alveolar air, diminished alkali reserve of the blood serum and abnormal acidity of the urine.