The effect of intravenous infusion of glutamate on edema formation after a freezing lesion in rats is reported. Twenty-four hours of continuous intravenous glutamate application led to a significant increase of hemispheric swelling, and of the water and sodium content as compared with animals receiving infusions of physiological saline after trauma. The results suggest that glutamate entering the e.c. space together with the edema fluid causes additional cytotoxic edema as a consequence of an enhanced glutamate uptake by the glia. Therefore, the use of amino acid infusions containing glutamate for parenteral nutrition may present an additional risk for neurosurgical patients with a disturbed BBB.