The retention times of particulate digesta were measured in two captive dugongs, Dugong dugon (Muller 1776) using inert plastic markers. The mouth-to-anus retention times (146-166 h) were similar to those of the West Indian manatee, and much longer than those of most other herbivorous mammals. This slow gut passage rate may be explained by the dugong's long digestive tract, the low fibre level of the diet and the low food intake. Like the manatee, the dugong appears to have a digestive strategy that is atypical of hindgut fermenters: low-fibre material is retained for extended periods within the long hindgut and almost completely digested.