In the course of neurosurgical procedures, many instances occur during which the reduction of intracranial pressure would afford more adequate exposure, facilitate intracranial operation, and minimize iatrogenic trauma. Likewise, in neurological management of patients, transient episodes of cerebral edema, especially of a diffuse nature, may respond to agents or methods which decisively lower intracranial pressure. Various techniques for reducing intracranial pressure exist, ranging from simple drainage of cerebrospinal fluid to bony decompression of the skull to the use of relatively complex intravenous solutions. It is the last-mentioned technique with which we are here concerned. All hypertonic solutions operate on the same principle, with only minor variations. The creation of a hypertonic intravenous milieu causes a movement of water from the intracellular fluid of the brain to the extracellular fluid, thereby reducing brain mass and effecting a lower intracranial pressure. If the ionic agent used, however, has the capacity to cross