EXCESSIVE systemic water intake ("water intoxication") produces cerebral swelling in anesthetized animals1-3but little or no cerebral swelling has been reported in two previous studies on unanesthetized animals.4,5The present project was undertaken to try to resolve these discrepant results and to determine if hypo-osmolar cerebral edema could be produced in unanesthetized animals. The results demonstrate that in unanesthetized rats intraperitoneal water injection produces chemically evident brain swelling, which is proportional to the amount of water injected but is less in brain than in other organs. This paper presents and discusses the clinical manifestations and chemical responses of the brain to water intoxication and the companion paper presents the microscopic findings.6 Methods Male adult albino rats weighing 200 to 250 gm were divided into four groups. There was a minimum of 12 animals in each group. Control animals (group C) were injected with 5 units