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 has been developed that allows the universal application of known algorithms, irrespective of the clearance substance used, by normalizing the plasma concentrations with respect to individual body dimensions of adult as well as infant patients. In this respect, algorithms are established for clearance determinations using technetium-99m mercaptoacetyltriglycine which are based on steady-state studies as the reference. They allow the calculation of quantitative clearance values in infants and require the drawing of only one blood sample at any time between 25 and 40 minutes postinjection. The comparison with a combined-camera/two-plasma-sample technique performed in 46 children ranging in age from 9 days to 14 years (mean, 6.05 years) resulted in a standard deviation of 8.5% from the line of identity (r = 0.94). Moreover, this procedure also increases accuracy in adult patients, especially those with impaired renal function.