Indirect radionuclide renocystography (IRRCG) is a method for the detection of vesico-ureteral reflux by analysis of the activity-time curves over the kidneys and bladder during voiding of urine about 30 min after intravenous administration of a radioactive indicator. This paper presents a new method for detection of reflux by a statistical test, the magnitude of the reflux is evaluated by the reflux volume per 1.73 m2 body surface area. Residual urine volume and urine voiding efficiency are also calculated. In a retrospective study of 154 children examined for renal and urological diseases consisting mainly of urinary tract infections, vesico-ureteral reflux was found by IRRCG in 16% of the kidneys (23% of the children). Reflux volumes were below 10 ml/1.73 m2 in 90% of the children with reflux. The mode value of the reflux volume was 2 ml/1.73 m2. For a subgroup of 97 children, the results were compared with micturating cysto-urethrography (MCU). This showed that a negative IRRCG in conjunction with the renal mean transit time of the radioactive indicator determined by gamma camera renography could be used as a screening test for vesico-ureteral reflux when MCU was considered a true reference method. Hence, about 75% of the invasive and high radiation dose MCU can be replaced by the non-invasive and low radiation dose IRRCG. The discrepancies between the two methods and the reasons for them are discussed.