In an effort to provide insight into the mechanism of Ca2+-induced fusion of lipid vesicles, molecular dynamics simulations in the isobaric-isothermal ensemble are used to investigate interactions of Ca2+ with apposed lipid bilayers in close proximity. Simulations reveal the formation of a Ca2+-phospholipid "anhydrous complex" between apposed bilayers, whereas similar calculations performed with Na+ display only complexation between neighboring lipids within the same bilayer. The binding of Ca2+ to apposed phospholipids brings large regions of the bilayers into close contact (<4 angstrom), displacing water from phospholipid head groups in the process and creating regions Of local dehydration. Dehydration of the apposed bilayers leads to ordering of the phospholipid tails, which is partially disrupted by the presence of Ca2+-phospholipid bridges.