The Pseudomonas aeruginosa major constitutive outer membrane porin protein OprF, which has previously been shown to be a protective antigen, was targeted as a DNA vaccine candidate. The oprF gene was cloned into plasmid vector pVR1020, and the plasmid vaccines were delivered to mice by biolistic (gene gun) intradermal inoculation. Antibody titers in antisera from immunized mice were determined by enzyme-linked immunosorbent assay, and the elicited antibodies were shown to be specifically reactive to OprF by immunoblotting. The immunoglobulin G (IgG) immune response was predominantly of the IgG1 isotype. Sera from DNA vaccine-immunized mice had significantly greater opsonic activity in opsonophagocytic assays than did sera from control mice. Following the initial immunization and two consecutive boosts, each at 2-week intervals, protection was demonstrated in a mouse model of chronic pulmonary infection by P. aeruginosa. Eight days postchallenge, both lungs were removed and examined. A significant reduction in the presence of severe macroscopic lesions, as well as in the number of bacteria present in the lungs, was seen. Based on these findings, genetic immunization with oprF has potential for development as a vaccine to protect humans against infection by P. aeruginosa.