Recent studies have increased our knowledge of Entamoeba histolytica cell biology and gene regulation. In the ameba, dominant-negative mutations in the Gal/GalNAc lectin affect adhesion and cytolysis, whereas mutations in meromyosin affect cytoskeletal function. Studying these mutant proteins has improved our understanding of the role of these proteins in E. histolytica virulence. The characterization of the CP5 cysteine protease and the induction of apoptosis in host target cells has led to a better comprehension of the mechanisms by which trophozoites can lyse target cells.