Acute intracranial hypertension may respond to intravenous mannitol, but frequent administration can cause cerebral edema or renal problems. We evaluated the use of 20% glycerol administered intravenously as an alternative to mannitol. Intravenous glycerol and mannitol were equally effective in lowering acute elevations of intracranial pressure. The duration of effect was similar for both agents. Side effects of intravenous glycerol were related to concentration, rate, and frequency of administration. In severe encephalopathies, such as Reye syndrome, we recommend infusions of 20% glycerol or 20% mannitol at a dose of 0.5-1.0 gm per kilogram. Glycerol should be administered in 0.45% or 0.9% saline, no faster than 1.5 ml (3.3 mOsm) per minute.