During a study of red deer (Cervus elaphus) dispersion in Glen Dye, northeast Scotland, preliminary observations showed that heather (Calluna vulgaris) formed the largest proportions of the rumen contents of wild deer shot in the winter. The purpose of this work was to determine whether the proportions of heather in the rumen were reasonable estimates of those eaten. Although the relationship between the percentage dry weight of heather in the food and the percentage dry weight of heather in the rumen was curvilinear, the differences from a 45.degree. slope were small. The maximum difference (about 10%) was when there were small amounts of heather in the rumen that were found only in summer in wild deer; the maximum difference above 50% dry weight of heather in the rumen (typical winter values for wild deer) was only about 6%. These differences were relatively small, and the proportions of heather by dry weight found in the rumen were reasonable estimates of the previous day''s intake.