Cystic fibrosis (CF) is a common, lethal, inherited disease among Caucasian children and young adults. While the pathophysiology of CF includes many organ systems (e.g., gastrointestinal, reproductive, endocrine) the predominant cause of death is respiratory failure. Hyperviscous respiratory secretions and related chronic pulmonary infections lead to scarring and fibrosis of the lungs, deteriorating pulmonary function, and death, with an average CF life expectancy of approximately 29 years. The disease is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CFTR functions, at least in part, as an epithelial chloride channel which resides in the apical membranes of exocrine gland epithelial cells. It has been suggested that the fluid and electrolyte content of normal respiratory mucus is dependent upon CFTR chloride channel activity, and that failure to secrete chloride by CF cells results in diminished hydration of mucous, sputum hyperviscosity and the pulmonary sequelae of the disease. © 1994, Mary Ann Liebert, Inc. All rights reserved.