Cystic fibrosis (CF) is the most common fatal genetic condition in the Caucasian population and affects over 3,000 Canadians. Respiratory failure caused by chronic pulmonary infection is the primary cause of death in CF patients. The improved life expectancy of CF patients in the past several decades is due in part to the more aggressive use of antibiotics in the treatment of respiratory infections. However, there is currently no antimicrobial susceptibility assay that can predict which antibiotics will result in improved patient outcomes. Since Pseudomonas aeruginosa is known to grow as a resistant biofilm in the CF lung, antimicrobial susceptibility testing based on biofilm growth of P. aeruginosa may lead to different antibiotic choices that significantly decrease the pulmonary bacterial density of P. aeruginosa. A biofilm antimicrobial susceptibility assay thus has the ability to change the way antibiotics are chosen to treat CF patients and result in improved lung function and longer lives for all CF patients.