The efficient utilization of plant material by herbivorous animals is made possible by microbial fermentation of food residues in the alimentary tract. In the ruminant animal, fermentation occurs in the rumen prior to gastric digestion of the food and in the caecum prior to the elimination of undigested residues. The reactions occurring in the rumen and the effect of the end-products of those reactions on the metabolism of the animal have been extensively studied. However, the part played by the caecum in the metabolism of ruminants is not known as few studies of its function have been made. In this experiment the concentration and molar proportions of the volatile fatty acids (VFA), the concentrations of protein nitrogen and ammonia nitrogen, and the pH in the rumen were compared with those in the caecum over a 24-hr period.