Entamoeba gingivalis attacks on gum of man. It occurs in mouth of nearly 70% of human population. Entamoeba of course aggravates pyorrhoea by destroying tissues in gums. This species does not form cysts since it is directly transmitted from mouth to mouth by contact. Trichomonas is most common endoparasite of invertebrates as well as vertebrates. The disease caused by Trichomonas is trichomoniasis. Giardia (Grand old man of the intestine) is a parasitic flagellate of intestine of man and other animals. Infection is by uninucleate cysts, which pass out in the faeces and infect other persons through contaminated food and water. It interfere with normal digestive process.