Noionic contrast material could have particular value in pediatric urography because of the absence of osmotic diuresis and associated fluid loss. Excretory urograms were obtained in 23 children using metrizamide at 300 mg l/ml and administered at a dose of 2.2 ml/kg. The radiographs gave excellent urinary tract opacification without changes in serum osmolality. The calyces appeared sharp but undistended, there was increased occurrence of ureteral ridging, and the urinary bladders often remained undistended at the completion of the studied. The dense opacification attainable with isoosmolar metrizamide also gave the opportunity for performing urography with higher than normal kilovoltage and thus reducing radiation exposure to the child. Also in vitro studies demonstrated the significant radiation dose reduction possible with the higher kilovoltage technique.