Twenty-eight Rambouillet cross lambs (27.85 ± 2.91 kg) were used in a 74-d feedlot experiment to evaluate the influence of zilpaterol hydrochloride (Zilmax, Merck Animal Health) and enriched-Cr yeast (BioChrome, Alltech) supplementation on feedlot performance of lambs. Sheep were weighed and individually allotted in 1.2 × 2.5 m concrete floor pens. They were randomly assigned to 4 treatments as follows: 1) A 85% concentrate diet, contained 15.5% CP and 1.87 Mcal NEm/kg, and formulated from corn grain and soybean meal (Control); 2) Control added with 0.2 mg of zilpaterol hydrochloride/ kg BW during last 28 d in the feedlot (ZH); 3) Control plus 0.3 mg of Cr/kg DM (YCr); and 4) Control plus ZH and YCr (ZHCr). Results were analyzed as a completely randomized design with a 2 × 2 factorial arrangement. Pen was the experimental unit; data were analyzed with initial weight as a covariate in the model. Final body weight tended (P = 0.10) to be increased by ZH supplementation (45.4 vs. 44.1 kg). Average daily gain tended (P = 0.07) to be higher for lambs in ZH treatment (0.306 vs. 0.280 kg/d). Dry matter intake was not affected by treatment (P > 0.20). Gain/feed ratio was increased (P = 0.02) by 11% (0.236 vs. 0.213 kg/kg) with ZH supplementation. Yeast-Cr supplementation did not modify any variable analyzed (P > 0.20). No interaction of ZH x Yeast-Cr was observed (P > 0.20). It is concluded, that zilpaterol hydrochloride supplementation promoted feedlot performance of lambs, whereas chromium supplementation from enriched-Cr yeast did not shown benefits to feedlot lambs both alone or in combination with zilpaterol hydrochloride.