Ileal mucosal stem cells expressing the sodium-dependent ileal bile acid transporter (IBAT) have been successfully transplanted into the jejunum of rodents in projects aimed at creating a "neoileum" to treat bile acid malabsorption. To find optimal harvest sites for a dog model of stem cell transplantation, the exact location of peak IBAT expression in the donor ileum needs to be known. We therefore mapped IBAT function, IBAT mRNA, and IBAT protein in the ileum of Beagle dogs (N=3). Mucosal samples were taken every 5 cm in the ileum and every 20 cm in the jejunum of each dog. Sodium-dependent (active) and sodium-independent (passive) taurocholate uptake rates were measured using a standardized everted sleeve technique. IBAT mRNA concentrations were determined by semiquantitative reverse transcriptase-polymerase chain reaction and IBAT protein concentrations by fluorometric immunohistochemical analysis. The small bowel measured 208+/-17 cm (mean+/-standard error of the mean). Active and passive uptake rates were found to follow distinct distribution curves. Significant active uptake was seen only at the terminal 50 cm and peaked at 479+/-176 pM/mm(2). Depending on location, active uptake accounted for approximately half of the total uptake. IBAT mRNA and protein distributions corroborated uptake curves. The terminal 10 to 50 cm of ileum has the highest bile acid uptake capacity. This short segment appears to be the most promising donor site for ileal stem cell transplants to create a "neoileum" in dogs.