This report provides reviews of information on the transit of materials through the alimentary tract and on radionuclide retention and absorption. It considers data on health effects, principally in order to specify the target cells for cancer induction within the mucosal lining of the tract and to justify approaches taken to dose averaging within regions. Comparisons are made between doses calculated using the HATM and the Publication 30 model for examples of radionuclide ingestion for which absorption is assumed to occur in the small intestine alone. Examples are also given of the effect on doses of considering absorption from other regions and the effect of possible retention in the alimentary tract. This report also considers uncertainties in model assumptions and their effect on doses, including alimentary tract dimensions, transit times, radionuclide absorption values, and the location of targets for cancer induction.