Cystic fibrosis is the most common potentially lethal autosomal recessive disease of Caucasians, affecting 1 in 2500 newborns. Since the recent identification of the gene that is defective in patients with cystic fibrosis, a wealth of information about gene structure, the mutational basis of disease, and the function of the protein product has been derived. The product of the gene is a chloride channel that is regulated by adenosine 3′,5′-monophosphate (cyclic AMP)-dependent protein kinase phosphorylation and that requires binding of adenosine triphosphate (ATP) for channel opening. Several new approaches to drug therapy for cystic fibrosis are now emerging, and the possibility of successful gene therapy by transfer of the normal gene to airway epithelial cells is being vigorously pursued.