One hundred and eighty children undergoing CT examination were randomly allocated to receive meglumine diatrizoate, iohexol, or iopamidol as their i.v. contrast agent. Minor side effects were detected in 85% of children receiving meglumine diatrizoate, in 18% of those receiving iohexol, and in 36% of those receiving iopamidol. Because many of these minor side effects cause patient motion or delay scanning after contrast medium injection, they potentially degrade image quality. These findings are an indication for the use of low osmolarity contrast agents for i.v. use in pediatric CT imaging.