Stagnant or blind-loop syndrome includes vitamin B12 malabsorption, steatorrhea, and bacterial overgrowth of the small intestine. A case is presented to demonstrate this syndrome occurring after small-bowel irradiation injury with exaggeration postenterocolic by-pass. Alteration of normal small-bowel flora is basic to development of the stagnant-loop syndrome. Certain strains of bacteria as Bacteriodes and E. coli are capable of producing a malabsorption state. Definitive therapy for this syndrome developing after severe irradiation injury and intestinal by-pass includes antibiotics. Rapid symptomatic relief from diarrhea and improved malabsorption studies usually follow appropriate antibiotic therapy. Recolonization of the loop(s) with the offending bacterial species may produce exacerbation of symptoms. Since antibiotics are effective, recognition of this syndrome is important. Foul diarrheal stools should not be considered a necessary consequence of irradiation injury and intestinal by-pass.