Publisher Summary This chapter discusses the temperature and pH sensitive liposomes for drug targeting. The use of hyperthermic for the purpose of drug targeting is discussed. Possible advantages of hypothermic targeting include (1) less damage to normal tissues by cooling than the damage seen with heating and (2) greater retention time of drug at the release site as a consequence of reduced blood flow. In vivo, such liposomes preferentially release encapsulated drug in a locally heated target area. When liposomes containing either tritiated methotrexate or cis-dichlorodiammineplafinum (II) (PDD) were administered to tumor-beating mice and the tumor locally heated, greater uptake of radioactive drug and greater local tumor control were observed compared to mice treated with systemic free drug and local heat. Based on the results with temperature-sensitive liposomes, containing PDD, especially the augmented drug uptake in tumors, the delay in tumor growth, and the potential decrease in nephrotoxicity, one considered the future of such targeting to be promising. Membrane fusion under moderately acidic conditions is responsible for the infection caused by a number of enveloped viruses and for the fusion that occurs when the virions are exposed to acidic pH in endosomes.