The effects ofAscaris lumbricoideson the human host are not known with any degree of accuracy. As infestation withAscarisis widespread in tropical countries and in some parts of the United States and often represents a major sanitary problem, it was thought desirable to determine the clinical condition of a group of patients infested with this worm. An excellent opportunity for such an investigation was available in Tennessee as several thousand persons withAscarisinfestation were found in an investigation of the common human intestinal parasites. ThatAscarismay cause serious surgical conditions is not questioned. There are numerous reports from all parts of the world of intestinal obstruction due to the worms becoming matted together into a mass and blocking the small intestine. There are also records of the worms blocking the common bile duct or the pancreatic duct or invading the appendix. The adult worms are