THE ACUTE rise of intracranial pressure associated with head trauma, brain tumors, and intracranial surgery brings in its wake grave results for the patient. Attempts at controlling this state have led to the use of many different hypertonic solutions. They are believed to act osmotically, by withdrawing water from the brain.1Several of these solutions have severe and undesirable side effects. The rediscovery of the efficacy of hypertonic urea solutions, freshly prepared and given intravenously, provided a comparatively safe method for clinicians to reduce intracranial swelling.2 In order to elucidate the mechanism underlying this treatment, it was necessary to find a suitable laboratory model. Triethyl tin sulphate (TET) poisoning in rabbits serves as a useful model for investigating water and electrolyte changes after hypertonic urea solutions have been given intravenously. The TET causes diffuse edema of white matter after a few days of intraperitoneal injection. The