In order to study the pathogenesis of radiculopathy, the authors investigated the effects of mechanical compression of the intraradicular blood flow in adult dogs using the electrochemically generated hydrogen washout method. The blood flow was more severly disturbed at the proximal side than the distal side when the nerve root was compressed, but when the clamp was released, the blood flow on the proximal side was almost completely restored, whereas the flow on the distal side did not recover and stayed at the reduced level. These phenomena can be explained both by the direction of blood flow in the radicular vessels and by the peculiar structure of the nerve root, which is soaked in cerebrospinal fluid.