The question of pathogenicity of Trichomonas intestinalis has long been debated without an apparent solution. The consensus of opinion among parasitologists at present seems to be in favor of nonpathogenicity of the flagellate. In fact, the majority of textbooks treat the infection as of minor importance. Barlow1 states that the increase of trichomonas is the result and not the cause of the diarrhea. Manson and Bahr2 refer to its presence as accidental and not due to a pathologic condition. Minchin3 claims trichomonas to be entozoic in the human intestine and a harmless scavenger rather than a parasite. However, Rhamy and Metts4 cite the incidence of local epidemic and endemic occurrence, and all the cases that came under their observation can be frequently traced to the same causes as acute and chronic diarrhea. Lynch5 emphasizes that it is a definitely pathogenic organism, and produces a mild enteritis manifested by intermittent diarrhea.