1. Surgical removal of the forestomach, the caecum or both the forestomach and the caecum, was performed on growing male golden hamsters (Mesocricetus auratus) given a low-or high-fibre diet.
2. In Expt J, 18 d after surgery, the hamsters which were given a concentrate before surgery were given an experimental low-fibre diet containing urea or [15N]urea (10 g/kg diet) for 9 d. In Expt 2, 5 d after surgery, the hamsters which were given a forage diet before surgery were adapted to an experimental high-fibre diet containing urea (10 g/kg) and dried Italian ryegrass (Lolium italicum) powder (400 g/kg diet) for 5 d, and 10 d after surgery, given a diet containing [l5N]urea (10 g/kg diet) for 9 d.
3. In both experiments, removal of the caecum resulted in a significant lowering of both weight-gain and the digestibility of the dry matter, and removal of the forestomach resulted in a significant decrease of both accumulation of 15N in the body protein and proportion of l5N retained in the body protein as a proportion of the administered dosage.
4. The effect of removal of the caecum on the utilization of [15N]urea was not apparent in Expt 1, but the utilization of [15N]urea was significantly lowered by removal of the caecum in Expt 2.
5. These results suggest that the caecum may play a more important role in food utilization than the forestomach. However, the forestomach of the golden hamster plays a significant role in the utilization of dietary urea. It is presumed that the role of the caecum in the utilization of urea may vary under different dietary conditions.