Thirty-six White-headed Mutton sheep x Polish Merino crossbred lambs weighing about 23 kg were divided into two groups and fed two isonitrogenous complete pelleted diets with low (group L) or high (group H) metabolizable energy (ME) levels. The animals were fattened to a final Hveweight of about 37 kg. Average daily gains in groups L and H were 220 and 242 g; intake per kg gain was: 55.7 and 53.8 MJ ME, 702 and 624 g of crude protein, respectively. Mean daily clean wool fibre production was similar in both groups (3.78 vs 3.95 g). The ME concentration in the diets did not have a significant influence on carcass dressing percentage or morphological composition. The protein content in 1 kg of empty body weight with fleece (EBW) ranged from 19.58 to 19.89%, fat from 17.10 to 17.32 %, and energy value from 11.34 to 11.48 MJ in groups L and H, respectively. The utilization of ME available for growth (k_f) by lambs from groups L and H was similar (0.40 vs. 0.43). Animals from group H deposited significantly (P<0.05) more protein in EBW gain (40.2 g/d) than lambs from group L (37.2 g/d).