Two experiments were carried out on 212 male Polish Lowland lambs fed a diet containing about 17% crude protein (group C), according to the Polish feeding standards, or a diet with the crude protein content reduced to 14% in the DM (group L). The lambs ate approximately 80% of the DM and 72 to 94% of the crude protein recommended by Polish standards. Comparison of the amount of protein digestible in the intestine with INRA feeding standards showed that in all of the groups the PDI requirement was exceeded by 5 to 24 per cent. The proportion of total N passing to the duodenum to N ingested was similar in groups C and L (91.5 vs 101.6%, respectively). No significant differences were found in the daily gains of lambs from groups C (237 and 240 g) and L (226 and 238g), while protein utilization in the L groups was significantly better (P≤0.01) than in the C groups (675 and 580 vs 770 and 662 g/kg gain, respectively). The carcass composition of the lambs was similar, with a slightly higher (P ≤ 0.05) proportion of separable fat in the carcasses of group L (16.5 vs 15.2% and 16.6 vs 14.7% in experiments I and II, respectively), while wool production was somewhat lower in this group than in group C.