Sterically stabilized (Stealth(R)) liposomes, in which the surface of liposomes has been altered, have been developed through the use of glycolipids (principally monosialoganglioside GM(1)) or polymers (principally polyethylene glycol). The resulting surface is more hydrophilic, and less able to bind opsonins from plasma. This results in liposomes which have decreased uptake into the mononuclear phagocyte system (MPS), increased circulation half-lives, increased stability to contents leakage, and dose-independent pharmacokinetics. These are significant advantages compared to conventional liposome formulations for use of liposomes in a number of therapeutic applications.