In most epithelial tissues Cl(-) transport relies on the cystic fibrosis 
transmembrane conductance regulator (CFTR) which has dual function as a Cl(-) 
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(-) and 
Na(+) and impaired secretion or absorption of electrolytes in cystic fibrosis. 
However, the CFTR mutation delta F508 is the most common reason for the 
frequently inherited disease among the Caucasian population. Maturation and 
processing of delta F508-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 delta F508-CFTR can be enhanced, and may 
lead to the development of new pharmacological tools for the treatment of cystic 
fibrosis.