2. To determine the effect of GH on pulmonary function. Pulmonary function tests, including FEV1, FVC and PImax and PEmax (for estimation of respiratory muscle strength), will be measured at baseline and every 6 months in all subjects. We will document inpatient admissions and outpatient antibiotic therapy during the study. Baseline pulmonary function will be analyzed as a covariate to determine whether children with good pulmonary function achieve greater benefit than children with poor pulmonary function. This specific aim tests the hypothesis that GH use improves pulmonary function in CF children regardless of level of pulmonary functions prior to using the drug.