The aim of this work was to determine the expression of cyclooxygenases (COX-1 and COX-2) during acute human renal allograft rejection. RT-PCR and immunohistochemistry were performed. The COX-2 mRNA was more abundant than COX-1 mRNA in the group with acute rejection (P <.001). The locations of COX-1 and COX-2 protein were consistent with the literature. Expression of COX-2 immunoreactive protein was higher in interstitial cells in the group with acute rejection than in the control group (P =.04). COX-2 protein was more abundant than COX-1 protein in the group with acute rejection, including podocytes (P <.001), proximal tubular cells (P <.001), collecting duct cells (P =.003), and interstitial cells (P <.001). In conclusion, COX-2 which is up-regulated during acute human renal allograft rejection, may play a role in renal inflammation.