Both the small intestine and liver account for 33 % to 49 % of total protein synthesis in the rat, from 3 to 105 weeks of life . Very little information is available, however, on the earliest stages of postnatal development. We describe here changes in protein synthesis before weaning in the small intestine and liver of one and five-week old lambs. The same large dose method was used for both ages to overcome problems that arise when measuring protein synthesis in these tissues (McNurlan et al., 1979