This issue contains the proceedings of the most recent Inter­ national Symposium on Brain Edema, the 5th in a series of confer­ ences starting 1965 in Vienna. The ever since increasing interest in this field may not only result from the fact that - in clinical terms - the problem is not solved yet, but also from the many fascinating physiological and biochemical questions remaining. Moreover, the rapid progress of technical, physiological and bio­ chemical developments provides a permanent challenge to probe the subject with better and better resolution. The current proceedings provide many examples. It is safe to assume, that the history of brain edema research is familiar to most of its participants. Therefore, suffice it to remark that since the first histopathological recognition of brain edema as a separate entity among the multitude of intracranial space occupying lesions, progress in the understanding of its pathogenesis has not been straightforward. On the contrary, it has been complicated by confusing notions and concepts, some of which may have resulted from the elusiveness of the edematous changes in early histological studies, due to the inadequacy of the light microscope. Although brain edema occurs concomitantly in many pgtho10gica1 conditions of the brain, it has been suggested that its role is collateral only. Nevertheless, the potential of brain edema as a space occupying lesion is not trivial, since it raises intracranial pressure and eventually may result in lethal cerebral herniation.