Visualization of intracranial structures is of value in localization and general neurologic diagnosis. In addition to ventriculography with air (Dandy), the visualization of various structures by the injection of colloidal thorium dioxide (thorotrast) into the subarachnoid space has recently been reported. By the lumbar or suboccipital injection of from 5 to 8 cc. of colloidal thorium dioxide Radovici and Meller1 and Wustmann2 have shown the surface outlines of the brain, some of the cranial nerves, the brain stem and the spinal cord (encephalography and periencephalomyelography). This procedure is reported to have good possibilities. It is recommended that as soon as roentgenograms have been taken, the patient be put in the upright position and that spinal fluid be withdrawn by lumbar puncture; an appreciable amount of colloidal thorium dioxide can thus be removed from the body. Wustmann pointed out that when colloidal thorium dioxide is used in this way