Normal tissue toxicity is a major limitation to effective cancer chemotherapy. As tissuespecific antineoplastic drugs have yet to be developed, much research has focused on carrier systems for the targeted delivery of drugs. The liposome (lipid vesicles) has been a prime candidate as a drug carrier with targeting potential. They are composed of naturally occurring phospholipids and cholesterol (Chol) and are relatively easy to prepare. Injection of drugs such as methotrexate (MTX) entrapped in liposomes composed mainly of egg phosphatidylcholine (PC) and Chol resulted in a greatly extended circulating half-life for the drug, about 100 times as much drug remaining in the blood 4 hr after injection compared to free drug injected controls. 1 Ultimately, the vesicles accumulate in anatomical sites with high macrophage activity such as liver, spleen, and lungs. Although some therapeutic advantage is gained from such liposomes, a pressing need exists for a more specific targeting system.