Serial hippuran renograms were performed in pediatric allograft recipients in an effort to detect the onset of rejection following the initial 3 month post transplant period. The plots of the normalized effective renal plasma flows (NERPF) were compared with reciprocal of the serum creatinines. A strong correlation was noted between both values. NERPF could be predicted from the serum creatinine utilizing a logarithmic equation. However, there was no detectable difference between the onset of changes in the slopes of either variable. Therefore, serial hippuran renograms were no better than monitoring serum creatinine in detecting allograft dysfunction when performed at the frequency of the study.