Results are given from two digestibility trials in which the following three diets were fed to sheep: (i) grass only, (ii) grass+5 oz. cotton cake daily, (iii) grass+10 oz. cotton cake daily. In the first trial the average dry-matter content of the grass was low (approx. 14%), intake was low and the supplements were eaten in addition to the grass. In the second trial where the dry-matter content (approx. 20%) of the grass and the intake were higher, the cake supplements reduced herbage consumption. The feeding of cake did not have any significant effect on the dry-matter percentage in the faeces but depressed the digestibility of the dry matter, crude protein, crude fibre and nitrogen-free extract in the diets including cake and reduced their starch equivalent and total digestible nutrient values. No evidence was found to support the recommendation that undecorti-cated cotton cake should be fed to grazing animals.