Cystic fibrosis (CF) is a lethal inherited disorder affecting about 1 in 2,000 Caucasians. The major cause of morbidity is permanent lung damage resulting from ion transport abnormalities in airway epithelia that lead to mucus accumulation and bacterial colonization. CF is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that encodes a cyclic-AMP-regulated chloride channel. Cyclic-AMP-regulated chloride conductances are altered in airway epithelia from CF patients, suggesting that the functional expression of CFTR in the airways of CF patients may be a strategy for treatment. Transgenic mice with a disrupted cftr gene are appropriate for testing gene therapy protocols. Here we report the use of liposomes to deliver a CFTR expression plasmid to epithelia of the airway and to alveoli deep in the lung, leading to the correction of the ion conductance defects found in the trachea of transgenic (cf/cf) mice. These studies illustrate the feasibility of gene therapy for the pulmonary aspects of CF in humans.