Enhanced Na(+)-linked nutrient absorption has been demonstrated in the cystic fibrosis bowel and may contribute to the dehydration of the luminal contents. The ability of loperamide to inhibit glucose transport was therefore assessed in jejunal biopsy specimens from children with cystic fibrosis by measuring the increased short-circuit current associated with active glucose absorption using a mini-Ussing chamber technique. The presence of loperamide in the luminal solution reduced the rise in short-circuit current induced by glucose over the range of concentrations tested (2.5 to 40 mmol.L-1). This finding suggests that the enhanced Na+ absorption, which is a feature of cystic fibrosis, is amenable to treatment and can be restored to normal levels. This result may have therapeutic implications for gastrointestinal function and may be applicable to other tissues where similar therapeutic approaches to reduce Na+ and thus water absorption are being pursued.