A sufficiently accurate quantification of renal function requiring only one plasma sample without an additional gamma-camera study has, until now, only been possible in adults. A new principle will be presented here allowing the universal application of known algorithms, regardless of the clearance substance used, by normalizing the plasma concentrations with respect to the individual body dimensions of the patients--for infants as well as for adults. In this respect, algorithms are developed for clearance determinations using technetium-99m mercaptoacetyltriglycine (99mTc-MAG3), which are based on steady-state studies as the reference. They allow the calculation of quantitative clearance values in infants, requiring only one blood sampling at any time between the 25th and the 40th min postinjection. The comparison with a combined camera/two-plasma-sample technique performed in 46 children aged between 9 days and 14 years (mean 6.05 years) resulted in a standard error of 8.5% from the line of identity (r = 0.94). Moreover, this procedure also increases the accuracy of results in adults.