Ischemia-reperfusion injury (IRI) in kidney transplantation is the major cause of delayed graft function (DGF), an event associated with an increased risk of acute rejection. The aim of this study was to evaluate T helper (Th) cell phenotype in renal transplants with DGF. T-bet (Th1), GATA-3 (Th2) and IL-17 (Th17) protein expression was investigated in pretransplant biopsies, DGF and acute tubular damage (ATD) caused by calcineurin-inhibitor toxicity. Intracytofluorimetric analysis of IFN-γ, IL-4 and IL-17 was performed to analyze Th1, Th2 and Th17 responses in peripheral blood mononuclear cells of recipients with early graft function (EGF) and DGF, before (T0) and 24 h after transplantation (T24). In pretransplant biopsies, T-bet(+) , GATA-3(+) and IL-17(+) cells were barely detectable. In DGF, T-bet(+) and IL-17(+) cells were significantly increased compared with pretransplant and ATD. More than 90% of T-bet(+) and less then 5% of IL-17(+) cells were CD4(+) . GATA-3(+) cells were increased to a lower extent. T-bet(+) /GATA-3(+) cell ratio was significantly higher in DGF. Peripheral CD4(+) IFN-γ/IL-4 ratio was significantly decreased in DGF, while CD4(+) /IL-17(+) cells did not differ between T0 and T24 in DGF. Our data suggest that DGF is characterized by a prevalent Th1 phenotype within the graft. This event might represent a link between DGF and acute rejection.