Eukaryotic protein trafficking involves the packaging of molecules into membranous vesicles that bud from a donor compartment, travel to a specific destination, fuse, and release their components 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) and target proteins (t-SNAREs) juxtaposes the membranes and results in an activated docked state and/or membrane fusion. VTI1a and VTI1b are putative mammalian SNARE proteins identified by sequence comparison with yeast SNAREs. In line with their involvement in vesicle transport, these molecules are expressed in a wide range of mammalian tissues. Vti1a, a possible t-SNARE, contains a C-terminal hydrophobic domain and several regions that may form coiled-coil structures. It exists in distinct syntaxin 5- and syntaxin 6-containing SNARE complexes within the Golgi apparatus. Inhibition of Vti1a blocks transport of G proteins to the cell surface and results in their accumulation within the Golgi. Thus, Vti1a functions in protein transport within the secretory pathway.