In this study we attempted to identify the factors involved in Epstein-Barr viral (EBV) infection among renal allograft recipients. We studied 68 renal allograft recipients hospitalized at the Imam Khomeini Medical Center from 2001 to 2004. Blood samples were obtained from the patients before renal transplantation and repeated every 3 months during the first year after transplantation. Enzyme linked immunosorbant assay (ELISA) tests were performed on these samples to determine if antibodies to EBV antigens, such as viral capsid antigen (VCA)IgM, VCAIgG or Epstein Barr neoantigen (EBNA)IgG, were present. The types of prescribed immunosuppressive agents and the incidence of acute allograft rejection were closely observed to define their association with EBV. EBV infection developed in 58 (85.3%) patients and active disease in 10 (14.7%). EBV was detected in 40 (58.8%) patients during the first year after transplantation. There was EBNAIgG seropositivity in 65 (95.6%) patients before transplantation; this number increased to 68 (100%) after transplantation. In contrast, VCAIgG seropositivity increased from 92.6% before transplantation to 96.9% after transplantation; whereas VCAIgM seropositivity increased from 17.6% before transplantation to 58.8% after transplantation. There were no statistically significant differences in the reactivation of EBV infection between the different immunosuppressive regimens, between the groups of acute rejection and no acute rejection, or between the groups that received and did not receive anti-lymphocyte globulin (ALG). We conclude that most EBV activation after transplantation may represent a secondary form of a preexisting infection and we could not find a clear association with a specific immunosuppressive regimen, including the use of ALG. Further investigation is thus required to elucidate the factors involved in the reactivation of the EBV infection in the transplant population.