Among diseases caused by parasites of the human body, intestinal parasitic infections (especially ascariasis, ancylostomiasis, necatoriasis, amoebiasis and giardiasis) are widespread and remain among the commonest infections in the world. In 5 villages from widely separated parts of India it was found that from 23% to 75% of the people were infected with roundworm, hook worm, pin worm, dwarf tapeworm and intestinal amoebas. Many villagers are consequently sick a great deal of the time. They are unable to absorb all the food the eat because of the damage done by parasites to the intestinal membranes and because part of their food goes to feed the worms and protozoa that infest their intestines.