Abstract. A careful comparison is made between the characteristics and structure of Balantidium minutum Schaudinn and the free-living coprozoic ciliate, Balantiophorus minutus Schew., as a result of which it is concluded that these two forms are identical and that Schaudinn was actually dealing with faecal samples contaminated by free-living coprophilic protozoa. All subsequent cases in which Balantidium minutum is alleged to have occurred are discussed and it is shown that in no one of them is the evidence inconsistent with the organism in question having actually been Balantiophorus minutus.