1. To determine the effect of GH on height, height velocity, body weight and lean body mass. We will measure height and weight using a standardized stadiometer and scale, respectively, every three months during the study. From these measurements we will calculate height and weight velocity and height and weight Z score. Lean body mass (LBM) will be measured by DEXA every six months. Baseline height and weight will be analyzed as covariates to determine whether children whose height and/or weight are at the lowest percentiles achieve greater improvement in height and weight velocity and lean body mass. This specific aim tests the hypothesis that GH significantly improves height, height velocity, weight, weight velocity and lean body mass in CF children irrespective of growth prior to starting the drug.