The ratio of blood ketone bodies 3-hydroxybutyrate to acetoacetate, once thought to be fairly constant, has been shown to vary from 0.6:1 to 4.8:1. In untreated, ketoacidotic patients, it is directly related to the plasma free fatty acid level. Administration of insulin lowers the ratio because the fall of blood 3-hydroxybutyrate occurs earlier and more rapidly than that of acetoacetate. During the treatment of ketoacidosis there is usually an initial increase of the acetoacetate which may persist at a high levelfor several hours despite improvement of the patient and falling 3-hydroxybutyrate and glucose levels.