Cystic fibrosis (CF) is the most frequent lethal genetic disease in caucasians. It behaves as an autosomal recessive disease. The CF gene encodes a protein named CFTR (for "Cystic Fibrosis Transmembrane conductance Regulator") which exerts multiple functions. One of the most important function is the regulation of sodium and chlorine transport in epithelia. Defects in this control induce dehydration of airway surface liquid, which results in recurring bronchopulmonary infections, and increases in Na and Cl concentrations in sweat, which constitutes the rationale for the sweat test. CFTR also participates in the regulation of inflammation. Over one thousand mutations in the CFTR gene have been reported, the most frequent of which is the absence of the phenylalanine residue at amino acid position 508 (delta F508).