The bacterial flora has been studied by direct sampling techniques at various levels in 25 cases of acute small bowel obstruction. The presence of coliform bacteria in the distal ileum below the level of obstruction and progressive increase of bacterial counts from the jejunum towards the distal ileum above the obstruction suggest that ingestion may not be the only factor of bacterial growth in the small bowel in acute intestinal obstruction. Moreover, indirect peritoneal contamination in 8 cases of long-standing acute small bowel obstruction indicates that possibly a combination of multiple factors like ingestion of food, retrograde spread from the large bowel, lymphatic and/or hematogenous spread are responsible for bacterial dissemination in and around the obstructed bowel.