One of the most exciting breakthroughs of the 90's in the fields of biochemistry, cell biology and neuroendocrinology is the identification of a novel family of proteolytic enzymes called mammalian subtilisin-like convertases. This family is comprised so far of seven distinct endoproteases responsible for the proteolytic excision of biologically active polypeptides from inactive precursor proteins. Six years after the initial observation of a structural conservation between a characterized yeast enzyme (kexin) and a human gene product (furin), it is now well accepted that one of these convertases, furin, has the enzymatic capabilities to efficiently and correctly process a great variety of precursors. Furin's ability to cleave precursors within both the exocytic and endocytic pathways will require sustained efforts in order to delineate all of its physiological roles.