Radionuclide renography showed an obstructed pattern in 6 patients with meningomyelocele without dilatation of the upper urinary tract or reflux when the bladder was filled to the volume that during previous urodynamic testing had resulted in an intravesical pressure of 40 cm. water but not when these patients were studied with an empty bladder. Therefore, this study indicates that treatment should be directed at avoiding long-standing intravesical pressure exceeding 40 cm. water in patients with meningomyelocele.