A Study of the Safety and Efficacy of Tobramycin for Inhalation in Young Children With Cystic Fibrosis

Inclusion Criteria: * Age at least 6 months and less than 6 years * Diagnosis of cystic fibrosis with 2 clinical features consistent with CF and confirmed by either sweat chloride \>= 60 mEq/L (by quantitative pilocarpine iontophoresis) or by genotype with 2 identifiable mutations consistent with CF. * One throat or sputum microbiology culture positive for Pseudomonas aeruginosa (Pa) within 2 weeks to 12 months prior to screening. * Informed consent by parent or legal guardian. Exclusion Criteria: * History of adverse reaction to anesthesia or sedation. * History of aminoglycoside hypersensitivity. * History of unresolved anemia (hematocrit \< 30%) or thrombocytopenia (platelet count \< 100,000/mm3). * History of hemoptysis with 30 days prior to screening. * History of abnormal renal function (serum creatinine \> 1.5 times the upper limit of normal for age). * History of clinically documented chronic hearing loss. * Administration of any investigational drug within 30 days prior to screening.