We have studied simple methods of analysing bile acids in human small intestinal aspirates, in order to assess their suitability for the routine clinical investigation of patients with steatorrhoea. Following extraction into methanol, samples were analysed qualitatively for bile acid deconjugation by thin-layer chromatography and quantitatively by the 3-alpha-hydroxysteroid dehydrogenase enzyme assay. These methods were found to give good recoveries, and to be sensitive, accurate, and specific, in addition to being sufficiently simple and rapid for routine diagnostic purposes. This diagnostic procedure was applied to the identification of patients with steatorrhoea due to the stagnant loop syndrome, and was compared with other tests for this condition, viz, study of the small intestinal bacterial flora, urinary indican excretion, and the Schilling test with added intrinsic factor. Three groups of subjects were studied; group I consisted of nine patients with steatorrhoea due to the stagnant loop syndrome; group II (disease control group) of six patients with an anatomical stagnant loop that was not causing steatorrhoea; and group III (normal control group) of 11 subjects with no known gastrointestinal disease. The screening of postprandial upper jejunal samples for bile acid deconjugation proved the most useful diagnostic test, being positive in eight out of nine patients from group I, but in none of those from groups II and III. At lower levels of the small intestine, bile acid deconjugation was found in subjects from groups II and III. The other three diagnostic tests discriminated poorly between subjects from group I and those from group II.