Increased intracranial pressure could be lowered by means of 250 ml 40% xylite (1,2,3,4,5-pentanpentol) in 17 patients, the average dosage amounted to 1.36 mg/kg, the lowering of the pressure to 54.4 plus or minus 18.4%. The effect lasted 109.5 plus or minus 35.4 min; the maximum occurring after 50.4 plus or minus 14.8 min. With the exception of 3 patients who complained of slight gastrointestinal disturbances, no side reactions were observed. Paralleling the lowering of CSF-pressure increased diuresis occurred amounting to 400% (including the infusion volume). The maxima of diuresis and lowering of CSF-pressure concur. Simultaneously we can see a highly significant lowering of urine potassium and a slightly significant lowering of sodium within the first 2 h, which after 3 h is clearly receding. There was no significant change in the values of serum electrolytes, bilirubin and transaminases (SGOT and SGPT); the residual urea was just a little lowered. The lowering of CSF-pressure after xylite surpasses the effect of the same dosage of sorbit and fructose.