Parameters of protein turnover were measured in sheep differing in postruminal secretion and reabsorption of nitrogen. The experiments were carried out with Polish Merino sheep (20-25 kg BW) fitted with rumen and re-entrant cannulas at the duodenum and the ileum. Two groups of animals (n=9) were fed with diets that were nearly isonitrogenous but differed in crude fibre (CF) content (CF in % dry matter (DM): Group 1, 14.7, Group 2, 24.9). As a result of the higher CF content, the intake of DM was lower in Group 2 than in Group 1 (616 vs 467 g x d^-1). In all carried out experiments (Sandek et al., 2001a) one of the three animals (No 1) was labelled with ¹⁵N by intraruminal infusion of ¹⁵N urea. Then duodenal digesta of this labelled animal was exchanged with digesta of an unlabelled animal (No 2) during a 48 h period. The N- and ¹⁵N flow through the intestinal tract, the N and ¹⁵N excretion in faeces and urine as well as the absorption rates were estimated in animal No 2 during that period. Using these data, kinetic parameters of protein turnover were calculated using the end-product method and the 3-compartment model. Intake of N (16.1 vs 11.7 g x d^-1 in Groups 1 and 2), net N absorption (12.3 vs 7.3 g x d^-1) and N balance (104 vs -56 mg x kg BW^-1 x d^-1) were higher in Group 1 (P<0.10). No difference were found in flux (1666 vs 1458 mg N x kg BW^-1 x d^-1), synthesis (1238 vs 1087 mg N x kg BW^-1x d^-1) or breakdown (1134 vs 1324 mg N x kg BW^-1 x d^-1) of protein. However, the efficiency of protein synthesis (N balance/synthesis x 100) was significantly higher in Group 1 (8.8 vs -5.2%) (P<0.10). The efficiency of protein synthesis correlated negatively with N secretion in the postruminal tract (r =-0.99; P<0.001) and with ileal flow of endogenous N (r =-0.95; P<0.01). In conclusion, a high intestinal N secretion adversely affects the efficiency of whole body protein synthesis in growing sheep.