. 2015. Effects of zilpaterol hydrochloride and zinc methionine on growth performance and carcass characteristics of beef bulls. Can. J. Anim. Sci. 95: 609Á615. Sixty beef bulls with a body weight (BW) of 314.79 16.2 kg were used to evaluate the effects of zilpaterol hydrochloride (ZH) and zinc methionine (ZM) on growth performance and carcass characteristics. The experimental design was a randomized complete block, with a factorial 2 )2 arrangement of treatments (ZH: 0 and 0.15 mg kg(1 BW; ZM: 0 and 80 mg kg (1 dry matter). The ZH increased (P B0.05) the final BW, average daily gain, feed conversion, carcass yield and longissimus dorsi area. Bulls fed ZH plus ZM had less (PB0.01) backfat thickness and intramuscular fat (IMF) compared with those fed ZH or ZM alone. The ZH increased (PB0.02) the meat crude protein content and cooking loss. It is therefore concluded that ZH increases growth performance, carcass yield, longissimus dorsi area, and meat crude protein. The interaction of ZM and ZH did not present additional advantages. The reason for the reduction in backfat thickness and IMF by ZH plus ZM is unclear, and implies that our knowledge of b-agonistic adrenergic substances and their interactions with minerals is incomplete. (1 BW; ZM : 0 et 80 mg kg (1 matie`res se`ches Á DM Á « dry matter »). Le ZH a augmente´(P B0,05) le BW final, le gain moyen quotidien, l'indice de consommation, le rendement de carcasse et l'aire du muscle longissimus dorsi. Les taureaux nourris de ZH et de ZM avaient une plus faible (P B0,01) e´paisseur de gras dorsal et de gras intramusculaire (IMF Á « intramuscular fat ») par rapport aux taureaux nourris de ZH seulement ou ZM seulement. Le ZH a augmente´(PB0,02) la teneur en prote´ines brutes de la viande et les pertes a`la cuisson. Par conse´quent, on peut conclure que le ZH augmente la performance de croissance, le rendement de la carcasse, l'aire du muscle longissimus dorsi et le taux de prote´ines brutes de la viande. L'interaction de ZM et de ZH ne pre´sente pas d'avantages supple´mentaires. La re´duction de e´paisseur de gras dorsal et du IMF par ZM et ZH ensemble demeure incomprise et souligne que nos connaissances des substances b-agonistes adre´nergiques et leurs interactions avec les mine´raux sont encore incomple`tes.