Liposomes containing pH-sensitive molecules facilitate site-specific drug release in response to the change of pH in the surrounding serum. They deliver drugs or gene fragments into the cytoplasm through the endocytotic pathway. Unlike plain liposomes, pH-sensitive liposomes effectively protect drugs and other encapsulated contents such as enzymes, plasmids, proteins and peptides from being potentially degraded at the lysosomal level. They have a wide range of clinical applications such as a carrier of potent drugs for cancer, pulmonary and infectious diseases, a vaccine adjuvant and a vehicle for contrasting agents during imaging. In addition, pH-sensitive liposomes also facilitate the transport of nucleic acids during gene therapy. DOPE liposomes containing PHC deliver their contents at the early endosome.