In order to assess whether the transplanted nephronic mass plays a role in the progression of chronic graft dysfunction, 83 well-functioning renal transplants were investigated. Plasma creatinine, creatinine clearance, renal volume, blood flow and renal vascular resistance were measured. The weight of the donor was considered as an index of the transplanted renal parenchyma and the weight of the recipient as an index of the required nephronic mass. To evaluate the adequacy of the transplanted nephronic mass, the ratio between the donor and the recipient's weight was calculated. This ratio showed a mean of 1.06 +/- 0.18 and a range between 0.63 and 1.6, indicating that a parenchymal mass between 30 and 80% of the physiologic one was transplanted in these subjects. Patients were divided into two groups: group A patients with a ratio > 1, group B patients with a ratio < 1. In group A, a regression analysis did not show any relationship between transplant age and creatinine clearance, renal volume, blood flow and renal vascular resistance as assessed by echo-color-Doppler ultrasonography. In patients with reduced nephronic mass, group B, there was a negative relationship between renal blood flow and transplant duration (p = 0.03) and a positive relationship between transplant age and renal vascular resistance (p = 0.01) and renal volume (p = 0.01). These data support the hypothesis that the difference in weight between donor and recipient may influence the outcome of the graft.