LL37 is a natural antibiotic, active against bacteria and fungi and some viruses. Here we show that three monoclonal antibodies (RB139, RB141, and RB142) are exclusively specific for citrullinated LL37, whereas RB140 recognizes both native LL37 and cit-LL37. None recognizes LL37 modified by carbamylation. These antibodies can represent previously unavailable tools to detect the presence of citrullinated LL37 in body fluids by ELISA in the course of autoimmune and infectious diseases.