Starting from the eleventh day of life, three groups of 48 suckling Polish Lowland lambs each were fed to appetite with meadow hay and a concentrate containing 16.7, 14.7 or 12.3% crude protein (CP) in dry matter (DM). Consumption of the concentrate decreased as the protein content decreased, while the proportion of hay DM in total consumed DM increased from 41 to about 43 and 46%, respectively. No statistically significant differences were found in body weight gains (male, 173, 134 and 146 g/day; female, 144, 134 and 136 g/day, respectively) or body weight of suckling lambs from day 28 of life to weaning. Utilization of DM and metabolizable energy (ME) per kg gain was similar (2.16, 2.17 and 2.08 kg DM and about 25 MJ ME), whereas protein utilization improved as its content in the diet decreased (322, 297 and 258 g crude protein/kg gain, respectively). No significant differences among the gains of 92 young rams (from 221 to 232 g/day) were observed in four groups of 23 rams each fed diets differing in their protein level (16 vs 14% CP in DM) and source (soyabean oilmeal (SBM) or rapeseed oilmeal (RSM), from a double - low variety). The utilization of feed DM was somewhat better in group that received SBM (S^H) than in the group receiving RSM (R^H) in the high protein ration (4.43 vs 4.67 kg DM/kg gain, respectively), while when the protein content was lowered, feed utilization did not differ between groups (4.54 vs 4.67 kg DM/kg gain, respectively). Protein utilization did not differ between groups receiving the same amount of protein in their diets, but was worse (P≤0.05) in group R^H (741 vs 639 and 634 g/kg) than in both groups fed a diet with a lower protein content (S^L and R^L). The lambs fed the rations with the highest protein level (16.7% in DM) grew somewhat more slowly during fattening (217 vs 232 or 227 g/day) and consumed significantly more feed (P≤0.05) than those given the feeds containing 14.7 or 12.3% CP in DM (4.83^a vs 4.30^b or 4.49^b DM/kg gain).