In the course of a neuroradiologic investigation of the brain, it is sometimes imperative to obtain unequivocal radiographic visualization of the third ventricle, the aqueduct of Sylvius, and the fourth ventricle. This can usually be done with gas as the contrast substance. Occasionally, however, gas will not enter the regions it is desired to visualize, or a small, gasfilled cavity cannot be clearly separated from the shadows of superimposed structures. This last difficulty can sometimes be resolved by laminagraphy. There will remain, however, a small number of cases in which even this modality, when available, will fail. It is possible to fill the small midline ventricular cavities with a contrast material of very high density, such as Pantopaque. When this is done, the ventricular outlines can be seen, clearly and distinctly, on radiographs. This technic has been called “positive contrast ventriculography.” While it has been known for almost thirty years (1), it has never attained widespread use in this country, so far as we can determine from a review of the literature. Readers who are interested in the historical background are referred to the papers by Bull (2) and Horwitz (3). Those who have written on positive contrast ventriculography describe different methods of conducting the procedure(2–4). Itis preferably done under local anesthesia, in order to secure the patient's active cooperation, though general anesthesia may be satisfactory. In our experience, the decision to undertake positive contrast ventriculography is usually made at the time of gas ventriculography. Therefore, in most of our patients the procedure was done under general anesthesia. It is of interest to note that when positive contrast ventriculography has been done independently of gas ventriculography, the discomfort and febrile reaction have been minimal. Method Except in infants, it is necessary to have a surgical burr hole in the skull. This is usually already present, due to the fact that gas ventriculography will have been done previously. The patient is seated upright in front of a vertical fluoroscope, and is positioned so that the fluoroscopist can obtain a good lateral view of the skull. The neck and body are flexed, until the foramen magnum lies at a higher level than the vertex. The head is then rotated 45°, so that the side containing the burr hole is uppermost. A needle is introduced through the burr hole into the lateral ventricle, and 1 to 2 c.c. of Pantopaque is injected, the amount depending upon the estimated size of the third ventricle as seen on previous air studies, if such are available. If the head has been properly positioned, the Pantopaque will run along the superior and medial wall of the lateral ventricle and will come to rest in the anterior horn. The patient's head is then rotated back to the sagittal plane and his body is straightened up, but his head and neck are still held in flexion.