Some enveloped viruses such as influenza virus and human immunodeficiency virus type 1(HIV-1) enter cells via clathrin-mediated endocytosis and release their viral genome into the cytoplasm by fusion of the viral envelope with the cell membrane. However, the entry mechanisms of these viruses into cells are not fully understood. Until recently, entry of HIV-1 into CD4/CR expressing cells was believed to occur by fusion of viral envelope to the target cellular membrane at lipid rafts in a pH-independent manner. It has also been reported that HIV-1 entry into macrophages is mediated via lipid-raft dependent macropinocytosis. Recent studies demonstrate that HIV-1 enters cells via CD4/CR-mediated endocytosis and viral fusion with intracellular membrane compartments is enhanced by dynamin-dependent pathway.