The experiments were carried out on 8 one-year-old rams of about 45 kg body weight, 4 with a surgically isolated caecum pouch (250 ml) and 4 with an approximately 1 m long isolated colon loop. The animals were fed a basal diet containing 11% CP or supplemented with urea to 14 or 17% CP. To study the influence of hypo- and hypertonic solutions on nitrogen compound secretion, the isolated caecum pouch was washed with antibiotics and filled with 0.45, 0.9, 1.8 or 2.7% NaCl solutions. Samples were taken after 4h to determine secreted nitrogen compounds. Increasing the NaCl concentration from 0.45 to 1.8% had no effect, but at 2.7% it significantly raised the amount of total-N secreted into the caecum from 5.4 to 14.3; protein-N rose from 3.8 to 11.9 and urea-N from 1.5 to 2.8 mg/h for 0.45 and 2.7% NaCl, respectively. The influence of the CP level in the diet was studied at 0.9% NaCl solution in the caecum and colon. Increasing the level of CP in the diet from 11 to 17% caused an insignificant rise of total-N secretion into the caecum pouch from 5.6 to 6.1; protein-N from 3.4 to 4.7; urea-N from 1.6 to 1.7 mg/h and the blood urea-N level from 10.5 to 16.4 mg/100 ml, respectively. Animals fed diets with 11 or 14% CP secreted as follows into the colon loop: 3.8 and 4.3 total-N; 2.9 and 2.8 protein-N; 0.8 and 1.4 mg/h urea-N, with a concomitant blood urea-N level of 10.7 and 14.5 mg/100 ml, respectively for the diets. Injection of 40 ml 7.5 % urea solution into the jugular vein of each animal every hour for 5 h progressively increased the level of urea-N from 11 to 26 mg/100 ml. The respective values of urea-N secreted into the caecum pouch were 2 and 11 mg/h and into the colon loop 2.2 and 3.3 mg/h.