The T-13 spinal cord segment of dogs was compressed both acutely and chronically by means of a balloon catheter. The vascular permeability to protein was assessed using Evans blue albumin (EBA), and the dorsal column evoked potential recorded to monitor conduction failure. With acute compression sufficient to cause conduction failure there was a marked leakage of EBA from the intermediate gray matter, which spread into the dorsolateral white matter. The degree of edema was similar whether the compression was maintained or released. Chronic compression maintained over 4 to 5 hours did not increase vascular permeability, but following release of compression leakage of EBA occurred in the same cord locations observed with leakage from acute compressions. This increased permeability following release of chronic compression may result from reactive hyperemia. Dorsal column conduction returned after the release of both acute and chronic compression. The extravasated EBA was present both in the extracellular space and within cells. The results and their clinical application are discussed.