Publication 100 of the International Commission on Radiological Protection (ICRP) provides a Human Alimentary Tract Model (HATM) to replace the gastrointestinal (GI) model described in Publication 30. The HATM will be used for future calculations of dose coefficients and bioassay predictions, first in a series of publications on occupational intakes of radionuclides, and subsequently in revision of dose coefficients for public exposures. This paper compares dose coefficients calculated using the new model with current values calculated using the GI model for a range of radionuclides. Colon doses are lower using the HATM in all cases considered, in some cases by significant factors. Stomach doses tend to be lower, but are in some cases higher under HATM. The extent to which these changes in doses to gut tissues impacts upon the effective dose varies among nuclides, but there is a tendency for lower effective doses. Special-case applications of the HATM are also described, considering retention on teeth or in the walls of the small intestine. Although the effect of such retention on the regional tissue dose can be large, the effective dose is not greatly changed.