Balantidium coli is an intestinal parasite of pigs and human beings; however, infections by this ciliate in man are comparatively rare, as is indicated by the cases reported.1The organisms have been found also in the intestinal tracts of orangutans and monkeys.2Awakian3found a balantidium in wild rats in Moscow, Russia. It seems therefore reasonable to assume that this parasite is a potential hazard because of its universal distribution and its numerous hosts. In spite of the fact that the possibility for infection is great, the opportunity for proctosigmoidoscopic study of cases is not frequent because they are not readily recognized. The following case was extremely interesting to us: M. H., a white man aged 33, a farmer, poorly developed, entered the Creighton Clinic on Jan. 7, 1941 complaining of periodic attacks of diarrhea of seventeen years' duration. The onset occurred in 1924, while he was