Since the subject of intestinal adaptation was last reviewed (16, 20, 97), there have been relatively few major advances but many useful minor additions and extensions which have helped to consolidate our knowledge of the field. The aim of this chapter is to summarise the results of a series of experiments which build up to our present state of knowledge. In doing so, the results of relatively old studies carried out some 15 years ago are briefly reviewed since they provide an essential background for, our current work. However, the article concentrates mainly on the new developments and in discussing these, areas of doubt and controversy are emphasised.