The enzyme poly(ADP-ribose) polymerase (PARP-1) participates in the repair of DNA damaged by genotoxic agents such as oxygen-derived free radicals. If the allograft suffers pretransplant cold ischemia and subsequent ischemia-reperfusion injury (IR), overactivation of PARP-1 can be induced, which may lead to an increase in acute tubular necrosis (ATN) and a delay in total recovery of renal function (RRF) of the transplanted organ. We studied the nuclear expression of PARP-1 in tubular cells by immunohistochemistry with the monoclonal antibody PAR01 in 104 kidney transplant biopsies from allografts with ATN. In 50% of biopsies with ATN, >50% of tubular nuclei were PARP-1+; only 9.6% of biopsies were negative. The increase in the immunohistochemical expression of PARP-1 showed a statistically significant relationship with the duration of cold ischemia, with serum creatinine levels, and with the time required to achieve effective diuresis (P < .0001, Spearman test). Cold ischemia of >24 hours and serum creatinine levels >1.7 mg/dL showed a statistically significant relationship with the highest PARP-1 expression levels (2.83 +/- 0.4 vs 1.36 +/- 0.8, P < .0001, Mann-Whitney U test). We conclude that PARP-1 plays an important role in ATN and RRF and is related to the extent and severity of ATN and to the renal allograft function.