Furin is a dibasic endopeptidase responsible for the proteolytic maturation of many precursor proteins in the secretory and endocytic pathways of mammalian cells. The levels of furin expression in most cells are very low, and this has hampered attempts to identify the intracellular compartments in which endogenous furin is localized. We have used a specific antibody reagent to a sequence in the carboxy terminus of furin to perform immunofluorescent staining of mammalian cell lines. This antibody was sensitive enough to detect staining for furin in various cell lines. For the most part, furin staining was confined to a juxtanuclear structure characteristic of the Golgi complex. Analyses by video microscopy and confocal microscopy showed that the distribution of furin was distinct from that of mannosidase II, a marker of the Golgi stack, and most closely resembled that of TGN38, a marker of the trans-Golgi network. Therefore, our results suggest that endogenous furin is predominantly localized to the area of the Golgi complex, most likely within the trans-Golgi network.