Although normally a mixed nerve, intracranially the vagus separates into dorsal rootlets that contain afferent axons and ventral rootlets that contain efferents. Surgical procedures are described for exposing the ventral surface of the occipital bone at the level where the vagus passes through the posterior lacerated foramen. When the foramen is expanded medially and the dura lanced, the intracranial course of the vagus can be observed by use of an operating microscope. Under these conditions, either the efferent or the afferent rootlets can be severed selectively. When the dorsal rootlets are divided and the contralateral trunk is cut below the diaphragm, a selective bilateral subdiaphragmatic afferent vagotomy is produced with unilateral sparing of the efferents. Cutting the efferents intracranially has the converse effect.