Anthrax, a cosmopolitan acute infectious disease affecting animals and humans, is a category A bioterrorism threat agent because of the high resistance of Bacillus anthracis spores to adverse environmental factors and their easy production. In this work, we have obtained a representative panel of 20 monoclonal antibodies to the anthrax protective antigen, a key component of the pathogenic exotoxin. A sandwich ELISA for quantification of the protective antigen using these antibodies was developed. Six pairs of monoclonal antibodies are able to detect the protective antigen in blood serum with a detection limit of 1 ng/ml. © 2011 Pleiades Publishing, Ltd.