In the first of two experiments, four rumen cannulated wethers were used to determine the extent of rumen protein degradation in soyabean meal (SBM), rapeseed meal (RSM) and extruded field bean seeds (EFB), using the in sacco method. Rumen non-degradable N in SBM, RSM and EFB of total-N was 38, 29 and 48%, respectively. In the second experiment, four rams with cannulas in the duodenum were fed isoenergetic total mixed rations (TMR) containing similar amounts of protein truly digestible in the small intestine (PDI). TMR consisted of meadow hay and concentrate (50:50, DM basis) in which SBM, SBM+RSM and SBM+EFB were the main sources of protein. The highest, statistically significant (P<0.05) methionine and cystine concentrations in the duodenal digesta were found in sheep fed SBM+RSM diet, while the lowest - in those fed SBM+EFB diet. Significantly higher (P<0.05) flows of total N (33.49 g/day), non-ammonia N (33.08 g/day) and total amino acid (197.7 g/d) were observed in sheep fed rations with SBM + EFB.