A relationship between targeting of the protein CFTR (Cystic Fibrosis Transmembrane conductance Regulator) and cellular polarization has been observed in various types of epithelial cells. However, there are no reports on this in human exocrine pancreatic cells, which are functionally altered in patients with cystic fibrosis. The expression of CFTR and its targeting to apical plasma membranes was investigated during growth and polarization of human ductal pancreatic cancerous Capan-1 cells. Despite their neoplastic origin, the cancerous pancreatic duct cells of the Capan-1 line secrete Cl^- and HCO₃^- ions. We showed by electron microscopy, impregnation of cells with tannin and freeze-fracture that these cells become polarized during growth in culture, and are joined by tight junctions. The expression of CFTR and the various stages in its anchorage to membranes was followed using a specific polyclonal antibody, ECL-885, directed against a synthetic peptide mimicking one of the extracellular loops of CFTR. Qualitative and quantitative confocal microscopic studies showed that: (i) the expression of CFTR was constant during growth, irrespective of cellular conformation, (ii) the number of cells presenting CFTR anchored to membranes increased with time in culture, (iii) the rise in membrane-bound CFTR-immunoreactivity accompanied the polarization of the cells, (iv) CFTR anchored to plasma membranes was distributed regularly over the surface of non-polarized cells, but was localized only at the apical membranes of the polarized cells. Moreover, patch-clamp studies indicated the presence of few Cl^- cAMP-dependent conductance CFTR channels on unpolarized cells, and a larger number of CFTR channels on the apical plasma membranes of polarized cells. These results indicated that the anchorage of a functional CFTR to the plasma membrane is progressive and occurs in step with polarization of these human pancreatic duct cells in culture. We suggest that the targeting of CFTR to the apical membranes is directly linked to the process of cellular polarization.