Thirty-two Black-headed Mutton sheep x Polish Merino crossbred lambs weighing about 22 kg were divided into two groups and fed two isonitrogenous complete pelleted diets containing low (group L) or high (group H) metabolisable energy (ME) levels. The animals were fattened to a final liveweight of about 36 kg. Average daily gains in groups L and H were 228 and 250 g; intake per kg gain was: ME, 56.6 and 54.8 MJ; crude protein, 718 and 649 g, respectively. Mean daily clean wool fibre production was similar in both groups (3.66 vs 3.75 g). The concentration of ME in diets did not significantly influence dressing percentage or morphological composition of the carcass. The protein content in 1 kg of empty body weight (EBW) ranged from 18.6 to 18.8%, fat from 17.6 to 18.1%, while energy value from 11.25 to 11.55 MJ in groups L and H, respectively. The utilisation of ME available for growth (k_f) by lambs from groups L and H was similar (0.38 vs 0.40). Animals from group H deposited a little more protein in EBW gain (39.1 g/d) than lambs from group L (36.8 g/d).