Munc18-1 is a 67kDa mammalian orthologue to unc18 in C.elegans , which was first identified as a syntaxin binding protein. Deletion of Munc18-1 results in severely hampered exocytosis in neurons and chromaffin cells. Utilising RNA interference, we have established PC12 cells in which Munc18-1 is stably knocked down by more than 90%. Our secretion assays revealed a 40-70% decrease in Ca-dependent vesicle exocytosis in the Munc18-1 Knockdown (KD) cells. In addition there was also a 40-50% decrease in the proportion of docked vesicles within Munc18-1 KD PC12 cells. Analysis of the localization of syntaxin1 in Munc18-1 KD cells reveals a significant intracellular mislocalization compared to controls. Such syntaxin1 mislocalization was also nearly completely rescued upon reintroduction of Munc18-1 into the Munc18-1 KD PC12 cells. This clearly supports our hypothesis that Munc18-1 acts as a molecular chaperone to syntaxin1 to facilitate the transport of syntaxin1 to the cell membrane in PC12 cells.