Abstract:Fecal flora of 12 children undergoing bone‐marrow transplantation was monitored prospectively using comprehensive microbiological techniques. Diarrhea developed at least once in ten of the 12 children (83%), and a total of 24 episodes were recorded. Recognised gut pathogens were isolated from 11/21 (52%) diarrheal episodes where fecal specimens were obtained. Enteric pathogens identified included viral pathogens in 19% (rotaviruses, ‘enteric’ adenoviruses), parasites in 19% (cryptosporidium, Giardia lamblia) and cytotoxicC. difficile(14%). Excretion of clostridial species (including cytotoxin negativeC. difficile, C. innocuum) occurred in 90% of diarrheal episodes when no enteric pathogen was identified. These results suggest that infection is often responsible for diarrhea associated with bone‐marrow transplantation. Prophylaxis against enteric infection might reduce the morbidity and mortality associated with severe diarrhea in bone‐marrow transplanted children. (Aust NZ J Med 1989; 1