The wall of the alimentary canal of Scottish sheep from 2 hill farms was found to fluctuate in weight and total nitrogen content during pregnancy, but to increase rapidly and progressively in weight and total nitrogen content during lactation. The peak was reached at weaning, after which there was a rapid decline. The protein laid down in the wall of the abomasum, small intestine and caecum from the first third of pregnancy to the height of lactation is negligible when compared with the extra protein requirements for pregnancy and lactation. Histological observations agreed with these data, showing a hypertrophy of the alimentary canal during lactation followed by post-weaning atrophy and, in some instances, degeneration. There were differences in the data obtained from the 2 groups of ewes which we ascribe to the differing husbandry and conditions on the farms from which they came.