A significant fraction of the total cellular protein synthesis is devoted to the production of proteins destined to membranes or to the extracelluar space. All these proteins begin their journey through the exocytic pathway within the Endoplasmic Reticulum (ER) where they fold, oligomerize and undergo other post-translational modifications. All these processes are under a tight "quality control" schedule that prevents uncorrectly folded molecules from exiting the ER and eventually routes them back to the cytosol for proteasomal degradation. We are exploring this field with a wide range of techniques, with an emphasis on the processes of disulfide-bonds formation, degradation and quality control of protein folding in the ER.