Merino wethers were used to study adaptation to biuret and the effect of a 3-day interruption in feeding biuret to fully adapted sheep. N-retention and urinary biuret concentration were used as criteria. When fed 7g biuret daily in addition to a basal ration, adaptation was complete by about 3 weeks. When fed a growth ration supplying 10,5 g biuret per day, the exclusion of biuret from the ration of fully adapted sheep for 3 successive days did not result in any measureable adaptation.