Two lots of straw pellets (supplemented with 10% molasses), produced either with a 5 mm sieve in a hammer mill (lot A) or with a 12 mm sieve (lot B) from wheat straw, were tested with 4 sheep (wethers, average live weight 43 kg) and 4 bulls (average 170 kg). After carrying out a digestibility experiment, the mean retention time (mrt), the 80%-excretion of the markers and the transit time were ascertained with the help of 51Cr-EDTA and 103Ru-phenanthroline. The digestibility of carbohydrates (both crude fibre and N-free extracts) was significantly higher for the bulls than for the sheep. Mrt, transit time and 80%-marker excretion were ascertained as follows: (Table: see text) The better digestion performance of carbohydrates from pelleted wheat straw in bulls in contrast to the sheep is due to the longer retention time of the digesta in the digestive tract of bulls. In connection with the considerably higher ruminating capacity of cattle in comparison to sheep, a longer retention time of the straw particles (Welch, 1982) in the reticulo-rumen must be considered.