Tc-99m MAG3 scans were obtained in two neonates in whom previous Tc-99m DTPA scans had been interpreted as showing possible obstruction. In both patients, Tc-99m MAG3 provided superior diagnostic images and allowed obstruction to be excluded. The favorable dosimetry of MAG3, coupled with the fact that its clearance is two to three times higher than that of DTPA, makes MAG3 an excellent radiopharmaceutical for pediatric patients, particularly in those patients with impaired renal function and possible obstruction.