This review describes the therapeutic activity of Bacillus subtilis spores (Enterogermina) in the treatment of intestinal disorders associated with alterations in the qualitative and quantitative composition of the normal human intestinal flora. On the basis of the present knowledge of gastrointestinal microbiology and of the physiology fo this antidiarrhoeal microorganism, a mechanism of action of oral bacteriotherapy with B. subtilis is proposed. Advantages of the use of B. subtilis as an antidiarrhoeal microorganism are also discussed.