Oxygen free radicals are generated during the reperfusion of ischaemic organs. Several experimental studies have demonstrated that the damage produced by reperfusion can be prevented by a scavenger of free radicals. Furthermore, a significantly improved 5 year graft survival rate after cadaveric renal transplantation has been reported in patients treated with scavengers of free radicals (Land et al., 1993). Therefore, a question remains to be answered: whether a routine monitoring of the radical-mediated reperfusion injury with renal transplantation is useful, and whether there is a necessity for a generalized protective treatment in transplant patients. In a prospective trial, we evaluated a group of eight patients during and after renal cadaveric transplantation (three men, five women), using the chemiluminometric measurement of serum free radicals and NO. The serum quantities of free radicals and NO were significantly increased after reperfusion of the transplant kidney (p < 0.02). The mean time of noticeably increased levels of serum free radicals was 4.8 +/- 1.2 h after reperfusion. The results thus showed an increased liberation of free radicals in the peripheral blood of transplant recipients as possible evidence of free radicals-mediated reperfusion injury in renal transplantation. The generation of free radicals measured by chemiluminescence allow a controlled therapy to decrease the generation of free radicals with antioxidants during the early transplantation period e.g. in older recipients.