Abstract. Macrophages in the lamina propria at the tips of small intestinal villi in 41 of 5 1 macaque monkeys were filled with eosinophilic, autofluorescent, periodic acid-Schiff-positive globules, hematoxyphilic and Feulgen-positive granules, vacuoles, and iron and lipochrome pigments. The Feulgen-positive granules were seen ultrastructurally in macrophages of nine of 15 clinically normal macaques and baboons. Four of the 15 had similar granules in the intercellular spaces of the epithelium. Ultrastructurally, the eosinophilic globules were electrondense phagolysosomes; the Feulgen-positive granules resembled nuclei of lymphocytes in various stages of pyknosis. Cytoplasmic organelles enclosed in rnembrane-bound vacuoles were present in the intercellular spaces of the epithelium of one monkey. Similar organelles were phagocytized by macrophages in another monkey. Feulgen-positive granules have been reported in villi of normal rodents. In all other species, including man, degenerating nuclei called "karyolytic bodies" and other evidence of enterocyte or lymphocyte degeneration have been considered abnormal concomitants of irradiation and antimitotic therapy. The significance of the findings in monkeys is not known, but they may represent a subclinical disease process.A characteristic histologic finding in necropsied macaque monkeys (Macaca) and baboons (Pupio) is many macrophages in the tips of small-intestinal villi. These cells contain cytoplasmic inclusions, such as pigments, eosinophilic globules, vacuoles, and basophilic granules. Such cells have not been reported in man [6,8, 291, and in the author's experience are not common in the villi of New World monkeys and domestic animals. Macrophages containing phagocytized nuclear debris have been described in the tips of villi of normal laboratory rodents [l, 5 , 211. The significance and morphogenesis of these "karyolytic bodies" in these species have not been established. T h e karyolytic bodies in small and large bowel, however, have been considered a significant lesion in several species with various diseases [7, 10,14,15,19, 261. They were considered significant effects of proton irradiation in Macaca mulatta [lo]; the authors seemed unaware, however, that such bodies also occur in macaques that die of many different diseases, and in clinically normal macaques. Macrophages with nuclear debris probably have been seen often in intestinal villi of 121