Thirty Polish Merino rams with average initial weight of about 20 kg were divided into 5 groups and fed five isonitrogenous and isoenergetic diets (about 15% crude protein and 11 MJ metabolizable energy/kg dry matter) containing soyabean meal (S) or blue lupin seeds - sweet cv. Remik (R) and cv. Emir (E), semi-bitter-cv. Ignis (I) and bitter-cv. Mirela (M). Mean daily liveweight gains of lambs from groups S, R, E and I were similar (180-188 g), while those of animals from group M (175 g) were significantly lower (P<0.05). Lambs fed diets containing M used significantly more (P<0.05) crude protein and energy per 1 kg body weight gain. Mean daily clean wool fibre production did not differ significantly between groups (4.50-4.70 g) nor did fibre diameter (3.63-3.83 µm) or sulphur content in wool (3.15-3.29%). No statistically significant differences were observed between groups in regards to dressing percentage (47.7-48.9%) as well as lean meat (11.66-12.11 kg), fat (3.62-4.02 kg) or bone (3.61-3.91 kg) contents in the carcass and also in the chemical composition of empty body weight (EBW). The value of the metabolizable energy utilization coefficient available for growth (k_f) in lambs from groups S, R, E and I was similar (0.42-0.44), while in lambs from group M it was significantly lower (0.39; P<0.05). Furthermore, animals from group M deposited significantly (P<0.05) less protein in EBW, wool gain and total gain than animals from groups S, R, E and I.