The presence of anti-HLA antibodies in the serum of a patient result from an immune response produced during an immunizing event as transfusion, pregnancy or graft. These antibodies can be cytotoxic by activating the complement pathway via C1q and may cause organ rejection during the transplant. Some male patients awaiting kidney transplantation are seropositive for anti-HLA antibodies when they have no immunizing antecedent event. These antibodies are qualified as natural antibodies. Our work is to assess the cytotoxicity of natural anti-HLA antibodies in patients followed at the immunology laboratory of the blood transfusion service and hemovigilance (STSH) as part of the kidney transplant. Patients and methods. - We evaluated the cytotoxicity of HLA antibodies detected in male Moroccan patients without immunization history using C1q Screen One Lambda reagent for Luminex (TM) Results. - Non-immunized men were positive for HLA antibodies screening in 25.4%. These antibodies are not cytotoxic. Conclusion. - Our study showed a positivity rate of natural HLA antibody low than the literature (25.4% against 63%). It appears that these natural antibodies are not cytotoxic and their involvement in renal transplant remains to be determined. (C) 2016 Association Societe de nephrologie. Published by Elsevier Masson SAS. All rights reserved.