Twenty-six children underwent a total of 75 99TCm-DTPA scans. Two experienced operators, using different techniques were able to identify parenchyme in 77 of 111 kidneys. Parenchymal regions of interest were drawn by an entirely operator dependent and a relatively operator-independent technique. Transit time analysis, using a matrix algorithm, through the parenchyme of both normal and abnormal kidneys showed a high degree of correlation (tau = 0.595, P less than 0.001). The technique concurred in the studies for which the analysis could not be applied, generally due to poor technical factors or gross hydronephrosis with insufficient parenchyme to generate a time activity curve. Either technique may be used in clinical practice to identify renal parenchyme for further analysis.