The recovery of inulin, a naturally occurring beta (2-->1)-fructan isolated from Jerusalem artichoke (Helianthus tuberosus L.), in the small intestine of man was studied in ileostomy subjects. The ileostomists were given a low-dietary-fibre diet based on white wheat bread and virtually free of inulin, and the same diet with the addition of 10 g and 30 g inulin product respectively, and the recovery and mean transit time (MTT) of inulin were estimated by tracking inulin in ileal effluent. The recovery of inulin was approximately 87% at both ingestion levels. MTT was 4.9 (SE 0.6) h at an intake of 10 g inulin product decreasing to 3.4 (SE 0.3) h at an intake of 30 g inulin product. A significant change in the fructose:glucose ratio of inulin from ingestion (4.1) to recovery in ileal effluent (4.5-4.7) and a lower recovery of the glucose residue than of the fructose residue of inulin indicate that the low-molecular-weight inulins are more sensitive to hydrolysis than the high-molecular-weight fragments. The loss of inulin during passage through the small intestine is presumably due to hydrolysis by either acids or enzymes and to microbial degradation by the microflora permanently colonizing the distal small intestine. The concentrations of lactic acid (LA) and short-chain fatty acids (SCFA) in frequently collected ileal effluents on the control day were approximately 6 nmol/l and approximately 55 mmol/l respectively. During periods with inulin ingestion the concentration of LA increased to 18-26 mmol/l (P < 0.052), while the concentration of SCFA ran converse and decreased to 18-32 mmol/l (P < 0.023). The osmotic loads (68 and 204 mosmol/l) associated with the ingestion of inulin product caused minor malabsorption of low-molecular-weight sugars.