Wardrop (1960) has shown that the type of nutrition is more important than the plane of nutrition, in determining the growth rates of the fore-stomachs of the lamb, and that plant food is necessary for the normal development of these organs. Lambs fed solely on milk from birth had the development of their fore-stomachs retarded at about the level found in the 3-week-old grazing lamb. Once plant food was fed, the fore-stomachs reached normal proportions very quickly.It would appear that the end-products (or a specific end-product) of rumen microbial digestion of plant food are responsible for the normal development of the fore-stomachs, rather than the physical nature of the plant food (Warner, Flatt & Loosli, 1956;Flatt, Warner & Loosli, 1958). No such rumen microbial end-product or end-products has been isolated and shown to be responsible for the normal development of the fore-stomachs.Brownlee (1956) also showed that plant food was necessary for the normal fore-stomach development of calves, and this worker observed that various plant foods produced different degrees of rumen papillae development. He concluded that rumen papillae development was not necessarily associated with the development of the rumen as a whole but was aproperty of the particular plant food.Trautmann (1932), working with kids, showed that although the weights of the fore-stomachs were retarded by prolonged milk feeding, the normal histological age changes still proceeded in the rumen and reticulum, but the omasum remained in a juvenile state until plant food was fed. The histology of the omasum wall changed very rapidly once plant food was fed, and was normal in an 84-day-old kid which had received solid food for only 4 weeks prior to slaughter.In this paper a preliminary survey on the effects of type of diet on the histological development of the fore-stomachs of the lamb is presented.