Large amounts of granules, interpreted as secretory in nature, are found in the terminal web region of intestinal cells of freshly collected Ascaris suum. Morphologically identical granules are scattered throughout the apical half of the cell cytoplasm and appear to be formed at the lateral ends of the Golgi saccules. Silver-proteinate-stained sections indicate similar staining properties of glycoprotein or polysaccharide nature for the Golgi saccules and granules, the apical granules, and the cell coat. Unlike the microvillous border, lysosomes, multivesicular bodies, and some Golgi saccules, the secretory granules do not stain for acid phosphatase. Differences in secretory activity between intestinal cells from A. suum immediately fixed after collection and from parasites maintained in vitro for several hours are reported. The functional significance of this activity in digestive and absorption processes is discussed. Contrary to the large amount of work devoted to the secretory processes of intestinal cells in mammals and some parasites only scanty morphologic data are available on this subject for Ascaris suum (Kessel et al., 1961; Sheffield, 1964). The origin and the nature of secretory substances in intestinal cells of mammals have been the subjects of many investigations. The involvement of the Golgi apparatus in the production of cell coat material and the role of Golgi vesicles and lysosomes in the transport to the cell surface has been emphasized (Ito, 1969; Bennett, 1970; Bennett and Leblond, 1970, 1971; Rambourg et al., 1971; Whaley et al., 1972). Several hydrolytic and proteolytic enzymes have been located on or near the apical surface of A. suum intestinal cells (Lee, 1962a, b; Borgers et al., 1970; Gentner et al., 1972; Van den Bossche and Borgers, 1973; Beames et al., 1974). Recent observations in our laboratory indicated that the secretory status of A. suum intestine varied with the time of fixation after collection from the host and stressed the importance of working with parasites fixed immediately after removal from the host. The aim of this morphologic investigation is to describe the secretory activity of intestinal cells of freshly collected worms and to determine the nature and origin of the secretion products with the aid of ultrastructural cyto-