Cystic Fibrosis (CF) is caused by a defective gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP- and ATP-dependent Cl- channel and central regulatory protein in epithelial cells. The most common mutation inducing CF is ?F508 that impairs CFTR processing within the cell and prevents functional CFTR expression in the apical membrane. The aim of this study is to achieve a functional expression and insertion of wild type (wt) CFTR in the apical plasma membrane of human CF airway epithelia after wt-CFTR-mRNA transfection. The human bronchial epithelial cell line CFBE41o- stably expressing ?F508-CFTR forms polarized cell monolayers with a sufficient transepithelial resistance when grown on permeable filters. This allows functional measurements of transepithelial transport processes in Ussing chamber studies. In orientating experiments we determined the appropriate length of the wt-CFTR-mRNA poly(A)-tail for an effective and long lasting expression using the Xenopus laevis oocyte expression system. We showed that a 120 poly(A)-tail produces maximal increases in CFTR current, conductance and capacitance following cAMP stimulation. Subsequently, we carried out Ussing chamber experiments with CFBE41o- cells transfected with this wt-CFTR-mRNA. In contrast to the non-transfected cells, the transfected cells showed an increased CFTR current after CFTR activation by cAMP (100 mM). Thus, CFTR currents in wt-CFTR-mRNA transfected cells were comparable with cells natively expressing CFTR (16HBE14o-). The CFTR activation is sensitive to the specific CFTR inhibitor CFTRinh172, which decreased all parameters significantly.Furthermore, we determined the abundance of CFTR protein in transfected CFBE41o- cells by Western blot analyses and additionally detected CFTR molecules at the apical surface or nearby regions with immunofluorescence approaches. From these data we conclude that wt-CFTR-mRNA transfection could restore impaired CFTR function in CF epithelia.