Determination of cerebrospinal fluid shunt patency with water-soluble contrast medium is a simple, rapid, reliable, and safe technique. Since September, 1974, the authors performed 113 examinations. With the Spitz-Holter valve, only the atrial catheter can be studied, but, with the Pudenz valve and with the shunting devices that have a double-dome reservoir, both the proximal and the distal catheter can be visualized. Through the ventricular catheter a full ventriculographic study can be made, demonstrating ventricular size, malposition of the catheter, and the lesion that caused the hydrocephalus, or its evolution. The problem of collapsed ventricules, in which clinical and "manual" evaluation of the flushing device can give misleading findings, is emphasized. The injection of the atrial or peritoneal catheter in the pathological cases demonstrated its blockage, level of disconnection, malposition, sleeve, or cyst formation. Computerized tomography has only slightly decreased the number of these studies: when the ventricles are large, the examination with water-soluble contrast medium is still needed to demonstrate the exact level of malfunction. This demonstration has decreased the number of the total revisions complete changes of shunting systems, eliminating some unnecessary changes of normally functioning catheters.