Annexins of human placenta have been purified and characterized. In addition to annexins I to VI and II complex, two novel species of 45 and 68 kDa were obtained. Annexins V and II are most abundant. Phospholipase A2 inhibitory activity of annexin V is low in contrast to that of annexins I to VI, and it is best for annexin II complex. In vitro, annexins bind to liposomes to extents which depend on the type of phospholipid used. This induces liposome aggregation whereby Mix, PI, and PC liposomes preferably aggregate. This hinders PLA2 from its access to the substate. Our data suggest that substrate-depletion by annexins is rather the result of liposome cross-bridging than pure liposome surface coating.