Summary This article reports 50 cases of infections in U. S. Army personnel with the intestinal coccidium, Isospora hominis. A limited study of 15 cases of infection with this parasite and casual observation of 35 other cases is presented. An attempt is made to indicate the probability that observed symptoms were due to infection with Isospora hominis and that these symptoms may be disturbing to the patient, even though not serious. The data collected suggest that infection with this organism persists over periods of at least several months.