Serpins (serine protease inhibitors) constitute a class of proteins with an unusually wide spectrum of different functions at extracellular sites and within the nucleocytoplasmic compartment that extends from protease inhibition to hormone transport and regulation of chromatin organization. Recent investigations reveal a growing number of serpins acting in secretory pathway organelles, indicating that they are not simply cargo destined for export, but fulfill distinct roles within the classical organellecoupled trafficking system. These findings imply that some serpins are part of a quality control system that monitors the export and possibly import routes of eukaryotic cells. The molecular targets of these serpins are often unknown, opening new avenues for future research.