1. The technique of third ventricular catheterization and methylglucamine iothalamate ventriculography is described, and representative cases are illustrated. 2. This technique has proved to be useful in patients with occlusive hydrocephalus of various etiology. It can be performed with the patient supine, and no maneuvering of the patient is necessary. 3. The procedure is easy and safe if a few precautions are adhered to.