Doripenem 50% inhibitory concentrations (MIC50) and 90% inhibitory concentrations (MIC90) for multidrug-resistant strains of mucoid Pseudomonas aeruginosa (n = 200 strains), nonmucoid P. aeruginosa (n = 200), and Burkholdetia cepacia complex (n = 200) isolated from patients with cystic fibrosis were 8 and 32, 8 and 64, and 8 and 32 mu g/ml, respectively. Doripenem had somewhat better activity than established antimicrobial agents.