99mTc-iron complex was used in 35 patients (20 adults and 15 children) in an investigation into ureteric reflux without using a catheter. The results were compared with the findings on micturating cysto-urethrography. Agreement in the findings was observed in 56 of the 69 kidneys examined. In only four kidneys, showing reflux radiologically, was this not observed on the isotope examination; in view of the low radiation dose, the catheter-free isotope method can be recommended as the most suitable investigation. The need for serial investigations or contrast allergies are important indications for using this method. The relatively high frequency with which reflux shown by the isotope method could not be confirmed radiologically (nine kidneys) indicates that the isotope is more sensitive than the radiological investigation.