Mutations in the presenilin 1 ( PS-1 ) gene cause Alzheimer's disease (AD). These mutations alter the processing of the amyloid precursor protein (APP) by increasing the production of the fibrillogenic amyloid fragment, Abeta1-42/43. Since the secretase activities that process APP are localized in different intracellular compartments, it is likely that membrane transport is a key factor in the pathogenesis of AD. In this report we provide evidence for a direct connection between PS-1 and membrane transport. We show that the N-terminus of PS-1 binds to rab GDP dissociation inhibitor (rabGDI), a regulatory factor in vesicle transport. In PS-1-deficient neurons we found a 2-fold decrease in the amount of rabGDI associated with membranes. Our findings are compatible with PS-1 being a membrane receptor for rabGDI. This is in line with a role of PS-1 in the regulation of protein trafficking in the ER/Golgi, which can modulate the production of Abeta.