Tissues of Ascaris lumbricoides (variety suum), the large round worm of pigs, contain trehalose, a disaccharide composed of two molecules of glucose. Minces of various Ascaris tissues were incubated with C14glucose to determine the site of trehalose synthesis. Chromatography and radioautography were used to identify C14trehalose synthesized during the incubation period. It was found that the reproductive tissues of both male and female Ascaris possess a mechanism for trehalose synthesis. Intestinal tissue and muscle showed no capability for trehalose synthesis under conditions of the incubation. By incubation of Ascaris tissue homogenates with commercial trehalose it was found that only intestinal tissue was capable of hydrolyzing trehalose into two molecules of glucose. The significance of synthesis and degradation of trehalose is discussed with regard to the findings of previous investigations.