The time course of free radical reactions is evaluated by the authors. Within pretransplant patients as of their poorly functioning metabolism free radical overproduction may be observed, hence their antioxidant capacity decreases. When the graft is functioning well, the free radical-antioxidant balance of homeostasis is reestablished. During the early postoperative period, when symptoms (acute rejection, infection, acute tubular necrosis, cholestasis) appear, free radical reactions increase. The authors demonstrate, this is strengthened by the fact that the mediator [interleukin-6 (IL-6), C-reactive protein, serum amyloid-A], and enzyme levels that take part in the free radical processes rise. The monitoring of these parameters during the early postoperative period is a good early indicator for acute rejection and for the effect of therapy. During acute rejection just as during infection most of these parameters increased significantly compared to the healthy control. They show the activation of the immune system but they are not useful for differential diagnosis, with the exception of IL-6 which we measured in larger quantities during bacterial infection but not so in acute rejection. For the prediction of early renal graft function we used urinary enzyme levels (dipeptidyl-aminopeptidase, glutathione-S-transferase). Tissue damage is followed by enzyme increasing and antioxidant capacity depletion. With choosing of adequate tests, the perioperative redox homeostasis of the transplanted patients can be monitored and with dosing the antioxidants the uncontrolled forming of reactive oxygen metabolites can also be decreased and checked.