This is a randomized, double-blind, placebo-controlled, multicenter, parallel group comparison study designed to evaluate efficacy of chronic, passive antibody immunotherapy employing one of two doses of a mucoid exopolysaccharide Pseudomonas aeruginosa immune globulin, intravenous (human) (MEP IGIV) in cystic fibrosis patients with endobronchial colonization by mucoid Pseudomonas aeruginosa.