Since the first descriptions of the contaminated small bowel syndrome, controversy has raged about both its pathogenesis and the mechanism of the malabsorption which often accompanies it.1-4 One, still popular, theory is that in small bowel bacterial overgrowth the concentration of conjugated bile acids in the gut lumen is reduced, by bacterial deconjugation, to levels less than those required for adequate micelle formation. The result is malabsorption of fat. However, there is as much controversy over the part played by bile acid deconjugation in the fat malabsorption of small bowel bacterial overgrowth as there is about whether malabsorption per se is an inevitable consequence of colonisation of the small bowel by colonic bacteria. Clearly, the presentation of this syndrome varies widely from patient to patient and a full investigation of the relation between events in the intestinal lumen and symptoms would therefore be very useful when considering treatment. However, there are many unresolved practical problems in this field, not least of which are the difficulties …