Young bulls of average live weight 130 kg, with rumen cannulae and re-entrant cannulae of the proximal duodenum, were fed on a diet of maize meal from whole plants, potato starch and a mineral mixture, containing 7.6% crude protein in DM (group IV). For three groups the diet was supplemented to contain about 17.5% crude protein with groundnut oilmeal (group I), grundnut oilmeal and urea, 27 and 31.2% of dietary N (group II) or urea alone (group III). The content of gross energy was similar in all diets. The amount of total N entering the duodenum in groups I to IV was 61.6, 59.2, 49.9 and 38.0 g/day and apparent digestibility of N in the stomachs was -0.4, 5.8, 21.6 and -44.4%. Total amount of amino acids in the duodenal digesta was, in the same order, 257, 261, 215 and 170 g/day, equivalent to 80, 116, 165 and 127% of intake. The ratio of the amounts of essential to nonessential amino acids was in feed 0.84 and in duodenal digesta in all groups 0.98. The amount of lysine in duodenal digesta was 1.5, 2.0, 3.5 and 2.5 times its intake in the same order of the groups.