The cystic fibrosis transmembrane conductance regulator (CFTR) is an integral membrane protein localized to the apical surface of epithelial cells that functions to facilitate Cl- transport. Certain mutations in the CFTR gene, including the most frequent ΔF508 mutation, lead to rapid protein degradation at the endoplasmic reticulum (ER). Recent studies indicate that both soluble and integral membrane proteins like CFTR can be targeted from the ER membrane to the cytosol, where degradation is catalyzed by the proteasome. The exact mechanisms underlying the ER-related proteolysis are not known. Sec61, an integral ER membrane complex, is a key component of the co-translational translocation machinery that binds growing polypeptide chains during their synthesis, and has been shown to associate with proteins selected for degradation. Based on these studies, we tested the hypothesis that CFTR interacts with the Sec61 complex, and Sec61 participates in preparing wild type and ΔF508 CFTR for degradation. We have shown that CFTR interacts with the Sec61 complex and the interaction is dependent on proteasome inhibition. CFTR/Sec61 complexes reach a maximum level at a time point when protein degradation proceeds at the highest rate. Only wild type CFTR was released from Sec61 complexes in order to permit further processing and maturation. In cell fractionation experiments CFTR and CFTR/Sec61 complexes could also be co-immunoprecipitated from the membrane and cytosolic fraction of the cells. Our results suggest a retrograde transport of CFTR through the Sec61 channel for degradation in the cytosol that involves the proteasome.