Three male sheep of about 25 kg body weight fitted with a cannula into the rumen and reentrant cannula in the proximal duodenum and in the distal ileum were used for this study. Sheep No. 1 was infused intraruminally with ¹⁵N urea ( 1 g/d, 95 atom% ¹⁵N) for labelling with ¹⁵N, Nos. 2 and 3 with unlabelled urea. A ll animals were fed 800 g DM /d of a hay and concentrate diet (40 : 60) containing 15.4 % crude protein and 15.3 % crude fibre, divided into 6 feeding portions per day. After reaching a quasi-steady state in the ¹⁵N level of animal No. 1, passage of total N and ¹⁵N throughout the duodenum and the ileum, N excretion in faeces and urine were estimated. On day 7 and 8 of the experiment the duodenal and ileal digesta were exchanged between the labelled animal (No. 1) and the unlabelled ones (No. 2, 3) according to the respective scheme. Digesta flow was measured directly during 48 h and 3% aliquots were sampled for analysis of N and ¹⁵N content. The contents of N and ¹⁵N were also estimated in faeces, urine and blood. The obtained data were used for calculation of the passage and absorption of exogenous N and the secretion, absorption and reabsorption of endogenous N in three digestive sections from mouth to proximal duodenum, from duodenum to ileum, and from ileum to rectum. The flow of total N , exogenous N and endogenous N decreased from duodenum to ileum and faeces, but the relative content of endogenous N increased from 36 to 54 %. N-secretion was highest in the first section of the digestive tract (9.9 g N/d = 60% of the secretion in total digestive tract) and absorption was highest in the second section (14.1 g N/d = 46 % of total absorption). Endogenous origin N was about 54 % of faecal N. Faecal loss, 2.0 g endogenous N/d, was only about 12% of the total endogenous N (16.5 g N) secreted into the lumen during the intestinal passage of digesta. Total reabsorption of endogenous N amounted to 88%. The results demonstrate the high dynamics of N metabolism during digestion in ruminants.