Fecal Examination for survey of natural prevalence of Balantidium coli was performed on 1,080 healthy bred pigs in Korea, and the positive rate was 56.2%. In order to observe if Balantidium coli might be a secondary invader after certain initiation of the intestinal lesions, the piglet groups preinfected with the protozoa experimentally were treated with salmonella cholerasuis, Trichuris, cold stress, HC1, and immunosuppressive drug respectively, but no relatios was found between them. Also the protozoa were not deteceted from the intestinal lesions spontaneously formed of 107 pigs which were checked in the slaughter house. According to the above results, Balantidium coli is not directly associated with the formation of any lesions in the pig`s intestine.