We will test our hypotheses by recruiting 40 CF children from five CF centers (8 per center) across the country. Patients will be randomly assigned to receive treatment with GH (0.3 mg/kg/wk) during the first 12 months, or during the second 12 months. All subjects will be followed every three months for the entire 24 months. Growth data and PFT data from the year prior to study will be obtained from the medical record for each subject. Our specific aims include: