Renal allograft biopsies (n=34) of two different populations of patients according to the immunological risk (high versus low-risk) have been compared retrospectively. The presence of polymorphonuclear leukocytes in peritubular capillaries was more frequent in the high-risk group. The C4d staining was positive in 10% of the low-risk patients and in 50% of the high-risk patients (P=0.03). There were more early graft loss, renal infarctions, interstitial hemorrhage, severe glomerulitis, neutrophilic glomerulitis and Banff III grade rejection in the positive C4d group. In conclusion, half of the immunized patients had a humoral rejection, patients with a C4d positive rejection had more early graft loss and more severe histological lesions.