In most epithelial tissues Cl<sup>–</sup> transport relies on the cystic fibrosis transmembrane conductance regulator (CFTR) which has dual function as a Cl<sup>–</sup> channel and as a regulator of other ion channels. More than 900 different mutations in the CFTR gene are the cause for defective transport of Cl<sup>–</sup> and Na<sup>+</sup> and impaired secretion or absorption of electrolytes in cystic fibrosis. However, the CFTR mutation ΔF508 is the most common reason for the frequently inherited disease among the Caucasian population. Maturation and processing of ΔF508-CFTR is defective which leads to expression of only very little but functional CFTR in the cell membrane. Understanding the processing and trafficking of CFTR may give a clue to the question as to how the expression and residual function of ΔF508-CFTR can be enhanced, and may lead to the development of new pharmacological tools for the treatment of cystic fibrosis.