Shunt blockage in valve-dependent hydrocephalic children is not always recognised, as symptoms may be non-specific and signs inconclusive. Valvography is a simple, easily interpreted technique for the investigation of shunt patency in children with Spitz Holter values in the shunt system. The technique affords a simple, rapid method of demonstrating patency at the cardiac end of the shunt. Fifty-one valvograms have been performed in 36 children. In 25 obstruction of the lower end was demonstrated. The unreliability of some associated signs is demonstrated. No serious complications have been observed and the technique has proved an invaluable addition to the practical management of these children.