Entamoeba histolytica (Gr., entos : within + amoeba : change + hist os: tissue + lysis: dissolve) is the causative organism of amoebic dysentery or amoebiasis in man. It is a microscopic endoparasite of man. It is commonly found in the upper part of the large intestine (colon) and is very often lodged in the liver, lungs, brain and testes. In its life cycle, it occurs in three distinct forms (i) trophozoite or magna form, (ii) precystic or minuta form, and (iii) cystic form. Trophozoite is the most active, motile and feeding form which is pathogenic to man. It lives in the mucous and submucous layers of the colon and feeds on these layers and erythrocytes.