Although the gross and microscopical characteristics of cerebral edema have been defined, no study has been made of the quantitative relationship of pathological anatomy to physiological dynamics during the development of this process. Light microscopy served to delineate many of the general anatomical features of brain edema, 1-10 but detailed high magnification observations were not possible until the advent of electron microscopy. 11-18 Until recently, the evaluation of intracranial dynamics was inadequate also, since a method had not been developed for the simultaneous determination of the physiological component units: blood, cerebrospinal fluid, brain water, and brain solids. 19 The necessary techniques were available for this study, however, and they were employed concurrently to correlate the anatomical and physiological events of experimental cerebral edema. Methods The experimental animal was the dog, unselected as to age and sex. The animals were anesthetized with sodium pentobarbital and an endotracheal catheter was inserted to