Pseudomonas aeruginosa mutants which do not express ferripyochelin-binding protein (FBP) on the cell surface have previously been isolated. These mutants were used to assess the role of FBP in virulence in an acute and a systemic animal infection model. In a mouse corneal infection model, the pathology of eyes infected with the mutant strains was significantly less than that of eyes infected with the parent strain. The mutants were also cleared more rapidly from the eye. In a burn infection model, the mortality rate in mice infected with mutant FBP-28 was much less than that of mice infected with the parent strain at an inoculum of 10(2) CFU. At higher inocula (10(4) CFU), the mortality rate was not significantly different but the survival time was dramatically longer with the mutant strain. Quantitative bacteriology of blood and tissue homogenates revealed that P. aeruginosa PAO could multiply in the skin and could also be cultured from the blood, livers, and spleens of infected mice. FBP-28 could only be cultured from the skin. Therefore, this mutant could colonize the skin but could not disseminate. These data indicate that functional, exposed FBP is required for virulence of PAO.