In an experiment conducted on 96 male lambs (3 groups of 32) fattened from 19 to 39 kg on diets containing various levels of crude protein (16 vs 14% in DM) and metabolisable energy (12.4 vs 12.7 MJ/kg DM) no significant differences in daily liveweight gain were noted (272 to 279 g). Feed utilisation was similar in all groups. A tendency (P>0.05) towards somewhat better protein utilisation (586 vs 674 g/kg) from isoenergetic rations was observed in lambs fed rations containing 14% CP than in those receiving 16% CP. Slaughter performance, morphological and chemical composition of the lambs' empty body weight, protein (18.3-19.8%) and fat (17.6-21.4%) deposition in empty body gain did not differ significantly among groups. Differentiating the level of protein (103-163 g/kg DM) in concentrates used to feed suckling lambs had no effect on liveweight gain during fattening (262-288 g daily).