Eukaryotic protein trafficking involves packaging of target molecules into membranous vesicles that bud from a donor compartment, travel to a specific destination, fuse, and release their contents into an acceptor compartment. Recognition between vesicle and acceptor membrane is mediated by the pairing of the integral membrane SNARE proteins. The stable interaction between vesicle proteins (v-SNAREs; VAMP1, VAMP2) and target proteins (t-SNAREs; syntaxin 1, SNAP-25) juxtaposes the membranes and results in an activated docked state and/or membrane fusion. With the identification of all SNARE family members in yeast, the research focus has turned to mammalian cells. Here, sequence analysis has identified additional SNARE proteins, including VTI1a and VTI1b. In line with their involvement in vesicle transport, these molecules are expressed in a wide range of mammalian tissues. VTI1b is a membrane bound protein whose localization overlaps with the cis/medial Golgi marker mannosidase II and the trans-Golgi marker syntaxin 6. VTI1b interacts with, and disrupts the localization of, syntaxin 5. Thus, VTI1b is thought to function in the regulation of post-Golgi vesicle trafficking.