In a study on the endogenous nitrogen excretion of immature sheep, it was found that young sheep reach their endogenous level on the 6th day, after having been on a standard ration of 14 per cent lucerne protein. The endogenous nitrogen excretion was found to be higher than in mature sheep, the average value for 4 months old wethers being .051 grms. per Kg. A formula for estimating the maintenance requirement of sheep was devised and its application tested. It was also shown that the basal metabolism of sheep can be predicted from the endogenous N, and that the figures arrived at agree very well with the values reported in the literature.