Bet1p is a type II membrane protein that is required for vesicular transport between the endoplasmic reticulum and Golgi complex in the yeast Saccharomyces cerevisiae. A domain of Bet1p, that shows potential to be involved in a coiled-coil interaction, is homologous to a region of the neuronal protein SNAP-25. Here, we used in vitro binding studies to demonstrate that Bet1p plays a role in potentiating soluble NSF attachment protein receptor (SNARE) interactions. Mutational analysis points to the coiled-coil region as necessary for Bet1p function, and circular dichroism experiments support this theory. In vitro binding studies were also used to demonstrate that a direct interaction between Bet1p and Bos1p is required for the efficient interaction of the vesicle SNARE with its SNARE target. Genetic studies suggest that the interactions of Bet1p with Bos1p are regulated by the small GTP-binding protein Ypt1p.