Our previous studies with anionic liposomes have suggested an apparent inverse relationship between the amount of blood proteins associated with liposomes and their circulation half-life.High levels of protein binding are associated with rapidly cleared liposomes, indicating that blood proteins play an important role in mediating cellular uptake.More recently, we have shown that this relationship holds for a number of variables affecting liposome clearance, including the lipid fatty acyl chain length and saturation, the cholesterol content, as well as the dose of the liposomes.The surface adsorption property of liposomes to blood proteins, therefore, is an important factor to consider when developing circulation-stable liposomes for systemic drug delivery.