Experiments were performed to assess the role of catecholamines in cold thermogenesis in warm- and cold-acclimated adult sheep. Urinary excretion of both noradrenaline and adrenaline increased in sheep exposed to cold. Propranolol (1 mg/kg) reduced cold thermogenesis in warm- and cold-acclimated sheep by 8% and 12% respectively. Noradrenaline and adrenaline infusions at 1 μg/kg min for 30 min had no significant effect on the rate of heat production of warm- or cold-acclimated sheep. Phenoxybenzamine (3.0 mg/kg) almost abolished cold thermogenesis in warm-acclimated sheep. Cold-acclimated animals treated with phenoxybenzamine were able to maintain homeothermy during severe cold stress. These findings support previous reports which suggest that catecholamines are involved in metabolic cold acclimation in the sheep, but indicate clearly that they have no direct thermogenic effect in cold-acclimated adults of this species.