Monoclonal antibodies against the elastase of Pseudomonas aeruginosa were produced from spleen cells of BALB/c mice primed with purified elastase of P. aeruginosa and P3-X63-Ag8-U1 myeloma cells. The six clones established generated antibodies which reacted with a 33,000-Da peptide and recognized four different elastase epitopes by a competitive binding enzyme-linked immunosorbent assay. The monoclonal antibodies designated as ELA-17 and ELA-42 that recognize two different epitopes reacted by dot-enzyme immunoassay and by Western immunoblotting with all clinical and International Antigen Typing Scheme strains of P. aeruginosa positive for elastase.