To examine the role of -adrenergic mechanisms in the regulation of endogenous glucose (Glu) production [rate of appearance (R_a)] and utilization [rate of disappearance (R_d)] and carbohydrate (CHO) metabolism, six horses completed consecutive 30-min bouts of exercise at ~30% (Lo) and ~60% (Hi) of estimated maximum O₂ uptake with (P) and without (C) prior administration of the -blocker propranolol (0.22 mg/kg iv). All horses completed exercise in C; exercise duration in P was 49.9 ± 1.2 (SE) min. Plasma Glu was unchanged in C during Lo but increased progressively in Hi. In P, plasma Glu rose steadily during Lo and Hi and was higher (P < 0.05) than in C throughout exercise. Plasma insulin declined during exercise in P but not in C; -blockade attenuated (P < 0.05) the rise in plasma glucagon and free fatty acids and exaggerated the increases in epinephrine and norepinephrine. Glu R_a was 8.1 ± 0.8 and 8.4 ± 1.0 µmol · kg¹ · min¹ at rest and 30.5 ± 3.6 and 42.8 ± 4.1 µmol · kg¹ · min¹ at the end of Lo in C and P, respectively. During Hi, Glu R_a increased to 54.4 ± 4.4 and 73.8 ± 4.7 µmol · kg¹ · min¹ in C and P, respectively. Similarly, Glu R_d was ~40% higher in P than in C during Lo (27.3 ± 2.0 and 39.5 ± 3.3 µmol · kg¹ · min¹ in C and P, respectively) and Hi (37.4 ± 2.6 and 61.5 ± 5.3 µmol · kg¹ · min¹ in C and P, respectively). -Blockade augmented CHO oxidation (CHO_ox) with a concomitant reduction in fat oxidation. Inasmuch as estimated muscle glycogen utilization was similar between trials, the increase in CHO_ox in P was due to increased use of plasma Glu. We conclude that -blockade increases Glu R_a and R_d and CHO_ox in horses during exercise. The increase in Glu R_d under -blockade suggests that -adrenergic mechanisms restrain Glu R_d during exercise.