The experiment was carried out on 3 pigs of 30 kg body weight each fitted with re-entrant cannulas into duodenum and ileum. One pig was given for 5 days ¹⁵N labelled and the others two unlabelled ammonium sulphate with diet. Total-N and ¹⁵N-labelled nitrogen balance and course of excretion with faeces and urine were estimated. Rates of absorption, secretion and reabsorption were determined using the method of digesta exchange between previously ¹⁵N-labelled and unlabelled pigs during the next 6 experimental days. Secretion in the upper part of digestive tract was 5.3 g/day (15% of intake) and absorption about 1 % of intake; in the small intestine corresponding values were 8.9 and 38.7 g N/day (25 and 110% of intake and in the large intestine 1.9 and 8.4 g N/day (5.6 and 24% of intake), respectively. Total absorption was to 134% of N intake, and the overall reabsorption of endogenous N compounds secreted into the gut lumen - 90%. The amount of endogenous N decreased from duodenum to ileum and to faeces (5.3,3.8,1.6 g N/day) while the relative proportion in comparison to the total N increased from 13 to 35 and 39% in digesta of duodenum and ileum and faeces, respectively.