Results of renal transplantation using cadaver donors (CAD) are usually inferior to those using living related donors (LRD). We have previously reported 100% 1-year CAD and LRD graft survival using adult cadaver donors and triple immunosuppression. In the present study glomerular and tubular function of 23 LRD and 22 CAD grafts (median ages 3.5 and 2.6 years) were compared during 3 years after transplantation. Glomerular filtration rate (GFR) and renal plasma flow were lower in CAD grafts but remained stable in both groups. The mean GFRs were 87.3 and 63.2 ml/min/1.73 m2 at discharge and 82.8 and 72.5 ml/min/1.73 m2 at 36 months in LRD and CAD grafts respectively. No significant differences were found after 6 months. tubular function was good in both groups. The only significant difference was in urate handling at 36 months (mean serum urate 396 mumol/l in CAD, 301 in LRD grafts, P < 0.05). Cyclosporin nephrotoxicity manifested as hyperkalaemia due to reduced distal potassium secretion and/or adrenal suppression. In conclusion, donor source had little effect on the development of progressive allograft dysfunction using adult CAD grafts and triple immunosuppression with CsA administered in three daily doses to preschool children.