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1. Donkeys sweat on exposure to heat and in response to intravenous adrenaline infusion.2. Thermal sweating was abolished by the adrenergic-neurone blocking agent bethanidine but not by atropine.3. Sympathetic decentralization (by preganglionic sympathectomy) abolished thermal sweating but adreno-medullary denervation had no effect.4. Exercise resulted in sweating from both sympathetically innervated and decentralized skin and from the innervated skin of animals which had previously undergone adreno-medullary denervation.5. Insulin-induced hypoglycaemia resulted in sweating from sympathetically decentralized skin and from innervated skin in two out of four animals. Adreno-medullary denervation abolished the sweat gland response to insulin administration.6. Cold exposure inhibited the response of innervated sweat glands but not that of decentralized glands to adrenaline infusion.7. It was concluded that heat-induced and exercise-induced sweating of the donkey is controlled by adrenergic nerves; adreno-medullary secretion may contribute to sweating during exercise, and that cutaneous blood flow is important in the response of the glands to humoral stimulation.