Background: Viruses can enter cells through several mechanisms, two common ones being clathrin-mediated and caveolin-mediated endocytosis. The clathrin pathway delivers viral particles to endosomes, with subsequent acidification of the endosome and endosome/lysosome fusion often a prerequisite for release of the viral genome into the cytoplasm. The caveolin-mediated pathway delivers virus initially into vesicles called caveosomes, which have a neutral pH, before viral uncoating occurs. Viral entry pathways can be examined by using various drugs to inhibit the different endocytosis pathways, as well as by siRNA technology to down-regulate expression of clathrin or caveolin proteins on the surface of host cells.