A study was carried out in the patients with intestinal tuberculosis and obstruction requiring surgery to determine the pathogenesis of malabsorption in this condition. Fifteen of the 20 patients studied had malabsorption, nine of 17 (53%) had intestinal bacterial overgrowth and 10 of 16 (62.6%) had free bile acids in their jejunal aspirates. In a comparable group of nontuberculus intestinal obstruction requiring surgery, six of seven (85.7%) had malabsorption, and four of five (80%) had both the bacterial overgrowth as well as bile salt deconjugation. Among a group of 10 patients with intestinal tuberculosis without significant obstruction, four were found to have malabsorption but only one had evidence of bacterial overgrowth and bile salt deconjugation. In contrast, only one of the 10 patients with extraintestinal tuberculosis and none of the 12 healthy, normal subjects had malabsorption. None had bacterial overgrowth or bile salt deconjugation in either group. Resection of the obstructing lesion corrected the malabsorption as well as the bacterial overgrowth and the bile salt deconjugation in all four patients tested with intestinal tuberculosis. Malabsorption in intestinal tuberculosis thus appears to be associated with obstruction rather than with the tuberculous process. Demonstration of bacterial overgrowth and bile salt deconjugation in the upper small intestine of patients with intestinal tuberculosis with obstruction and malabsorption indicate the presence of a stagnant loop syndrome.