In 14 children with indwelling ventriculoatrial or ventriculoperitoneal shunts, the need for continued shunt treatment was judged to be uncertain based on clinical symptoms and signs and CT scans. Ventricular outflow resistance (R0) was determined by implantation of a ventricular catheter and steady state infusion of artificial cerebrospinal fluid (CSF) according to the formula R0 = (Pp - P0)/Infusion rate, where P0 is the opening pressure in the lateral ventricle and Pp the plateau pressure recorded at that particular infusion rate. R0 was determined during general anesthesia and steady state ventilation was ensured by mechanical ventilator. Ventricular fluid pressure (VFP) and arterial blood pressure (ABP) were recorded by standard fluid pressure transducers. The cerebral perfusion pressure (CPP = ABP - VFP) was kept above 30 mmHg by reducing the infusion rate in cases of unacceptable increase in VFP. R0 was determined with the shunt clamped. During steady state infusion at the plateau pressure the shunt was unclamped to test shunt patency. Four children had normal R0 values with the shunt clamped. Their shunts were removed. They have done well clinically, and control CT scans have not demonstrated increased ventricular size. Three children demonstrated pathologic R0 values (above 12 mmHg/ml per min) that normalized after shunt unclamping; i.e. each had a well-functioning shunt. Seven children demonstrated increased R0 values even after shunt unclamping. Their shunts were replaced, and clinical improvement has been observed in 6 of them. Ventricular infusion tests appear useful to evaluate shunt dependence and function in difficult cases.