[Show abstract][Hide abstract] ABSTRACT: Recent literary data suggest that antibodies to HLA antigens undetectable by the standard complement-dependent cytotoxicity test may cause not only chronic, but also acute immunological complications after kidney transplantation. The aim of this study was to investigate the significance of non-cytotoxic antibodies to HLA antigens for the development of immunological complications and a worse graft prognosis after first kidney transplantation. Sera before and early after transplantation from 120 first kidney recipients were analyzed by flow cytometry (FCXM), ELISA and the standard complementdependent cytotoxicity (CDC) test. Pre-transplant FCXM negativity was related to a lower incidence of rejection episodes in the first posttransplant year (P<0.01). A significant association between acute rejection and the presence of antibodies to HLA class II antigens before and after transplantation was also found (P<0.05). Our study supports the findings of other centers of the detrimental role to the kidney graft played by anti-HLA antibodies undetectable by anti-HLA antibodies undetectable by the classical CDC test.