A human immunoglobulin G preparation, enriched in antibodies to lipopolysaccharide (LPS) Pseudomonas aeruginosa antigens (PA-IGIV) and murine monoclonal antibodies (MAb) to P. aeruginosa Fisher immunotype-1 (IT-1) LPS antigen and outer membrane protein F (porin), were evaluated for therapeutic efficacy in a guinea pig model of P. aeruginosa pneumonia. The concentration of antibodies to IT-1 LPS was 7.6 micrograms/ml in PA-IGIV and 478 micrograms/ml in the IT-1 MAb preparation. No antibody to IT-1 was detected in MAb to porin. For study, animals were infected by intratracheal instillation of IT-1 P. aeruginosa and then treated 2 h later with intravenous infusions of PA-IGIV, IT-1 MAb, or porin MAb. Control groups received intravenous albumin, and routinely died from pneumonia. Both PA-IGIV (500 mg/kg) and IT-1 MAb (greater than or equal to 2.5 mg/kg) treatment resulted in increased survival (P less than 0.01 to 0.001), and also improved intrapulmonary killing of bacteria. Porin MAb failed to protect from fatal pneumonia. IT-1 MAb treatment produced more survivals than did PA-IGIV treatment but only at dosages of MAb resulting in serum antibody concentrations greater than those achieved with PA-IGIV. PA-IGIV and IT-1 MAb demonstrated in vitro and in vivo (posttreatment guinea pig serum) opsonophagocytic activity for the IT-1 challenge strain. However, the polyclonal preparation required complement, whereas the MAb did not. We conclude that passive immunization with polyclonal hyperimmune P. aeruginosa globulin or with MAb to LPS antigens may be useful in the treatment of acute P. aeruginosa pneumonia. The relative efficacies of such preparations may be limited, however, by their type-specific LPS antibody concentrations.