Biochemical analyses of blood and cerebrospinal fluid of nine patients with diabetic ketoacidosis and impaired levels of consciousness were performed before and after four hours of intravenous therapy with insulin, saline, and bicarbonate. A comparison with previously reported data from a similar group of patients treated with insulin and saline alone revealed no significant differences in blood or cerebrospinal fluid with the following exceptions. First, the fall in CSF osmolality was significantly less after insulinsaline-bicarbonate therapy than in patients receiving only insulin and saline. Second, CSF pH values declined in both groups with therapy but were significantly lower in the group receiving insulin-saline-bicarbonate. Definite and progressive clinical improvement was noted in all nine patients from admission to discharge. It was concluded that the use of sodium bicarbonate did not discernibly alter the clinical course of the nine patients studied except for the unexplained slower decline in CSF osmolality. The use of NaHCO3 appears to be indicated primarily in situations in which prompt correction of metabolic acidosis is essential, e.g., to improve cardiovascular function.