Intravenous urography (IVU) and "Tcm DMSA scintigraphy are possible alternative diagnostic techniques in paediatric renal investigation. Radiation dose comparisons between them have been complicated in the past by the lack of paediatric data. In this study, evaluations relevant to children are used to compare estimates of effective dose from the two techniques. For the radiographie procedures, standard operating parameters and representative age-dependent values of entrance surface dose were established from recent literature. Conversion factors relating effective dose to entrance surface dose and dose-area product are presented and used to obtain values of effective dose for single radiographs of abdomen, kidneys and pelvis. Suggested IVU procedures consisting of four ("minimum") or eight ("average") radiographs were adopted to derive the effective dose for full IVU examinations. "Tc"1 DMSA dose estimates, taken from our published work using an administered activity schedule based on body surface area, are almost constant at about 1 mSv for all children. In comparison, mean IVU doses based on the "average" number of radiographs are similar to DMSA doses for infants 1 year) but may be twice as high for older children. Although the differences between procedures at this level of dose do not in themselves provide grounds for preference, when coupled with the lower diagnostic sensitivity of IVU they suggest limitations of this procedure for detection of a renal scar.