Interferon-alpha (IFN-alpha) is currently the only treatment for patients with chronic hepatitis C. Yet it can induce acute renal transplantation rejection possibly by stimulating humoral responses. We tested patient sera for detection of donor-specific anti-human leukocyte antigen (HLA) antibodies observing an increased panel-reactive antibodies value after IFN-alpha therapy. Then, we also investigated whether antiviral treatment with IFN-alpha was related to an increased and/or different production of class I and class II anti-HLA antibodies. Patient sera analysis performed by a cytofluorimetric method using flow PRA tests showed the appearance of new HLA-antibody specificities. This study underlined that INF-alpha therapy modifies a patient's immune profile; hence, it is recommended to confirm HLA-antibody specificities after treatment in order to protect recipients from enhanced rejection risk owing to a false-negative donor-specific cross-match.