The main pathology of cystic fibrosis results from obstruction of ducts in several organs by mucous secretions. The cause of this obstruction remains unclear. We have examined expression of the cystic fibrosis transmembrane conductance regulator (CFTR) and of the major pancreatic mucin, MUC1, in primary pancreatic duct and vas deferens epithelial cells, and in pancreatic duct cell lines. MUC1 is expressed at a high level in the primary ductal epithelial cells and at variable levels in different pancreatic adenocarcinoma cell lines. However, although the pancreatic duct is one of the sites in vivo where CFTR transcription is at its highest level, the majority of cell lines examined no longer express CFTR. Only one pancreatic duct cell line, Capan 1, expresses CFTR at a significant level; further, the level of expression is dependent on confluency. We have shown that salt stress alone is not sufficient to account for the build-up of mucous secretions in CF ducts.