Original Basic ScienceBackground. Complement activation in kidney transplantation is implicated in the pathogenesis of delayed graft function (DGF). This study evaluated the therapeutic efficacy of high-dose recombinant human C1 esterase inhibitor (rhC1INH) to prevent DGF in a nonhuman primate model of kidney transplantation after brain death and prolonged cold ischemia. Methods. Brain death donors underwent 20 h of conventional management. Procured kidneys were stored on ice for 44-48 h, then transplanted into ABO-compatible major histocompatibility complex-mismatched recipients. Recipients were treated with vehicle (n = 5) or rhC1INH 500 U/kg plus heparin 40 U/kg (n = 8) before reperfusion, 12 h, and 24 h posttransplant. Recipients were followed up for 120 d. Results. Of vehicle-treated recipients, 80% (4 of 5) developed DGF versus 12.5% (1 of 8) rhC1INH-treated recipients (P = 0.015). rhC1INH-treated recipients had faster creatinine recovery, superior urinary output, and reduced urinary neutrophil gelatinase-associated lipocalin and tissue inhibitor of metalloproteinases 2-insulin-like growth factor-binding protein 7 throughout the first week, indicating reduced allograft injury. Treated recipients presented lower postreperfusion plasma interleukin (IL)-6, IL-8, tumor necrosis factor-alpha, and IL-18, lower day 4 monocyte chemoattractant protein 1, and trended toward lower C5. Treated recipients exhibited less C3b/C5b-9 deposition on day 7 biopsies. rhC1INH-treated animals also trended toward prolonged mediated rejection-free survival. Conclusions. Our results recommend high-dose C1INH complement blockade in transplant recipients as an effective strategy to reduce kidney injury and inflammation, prevent DGF, delay antibody-mediated rejection development, and improve transplant outcomes.