Noradrenaline (3 µg/kg) injected into a lateral cerebral ventricle of sheep exposed to –15 °C caused a fall in plasma unesterified fatty acid (UFA) concentration. Acetylcholine with eserine (5 µg/kg of each) similarly injected in sheep at an environment of +5°C resulted in an increase in plasma UFA concentration. Intravenous injections of bethanidine, an adrenergic neurone blocking agent, did not prevent a marked increase in plasma UFA concentration after intraventricular acetylcholine and eserine. Denervating the adrenal medullae by cutting the right and the left splanchnic nerves also did not prevent a response to intraventricular acetylcholine and eserine. The combined effect of bethanidine and cutting the splanchnic nerves almost completely blocked the response to intraventricular acetylcholine and eserine. These results indicate that acetylcholine and noradrenaline may be the central neurotransmitter substances controlling plasma UFA concentration through the activity of the sympathetic nerves and splanchnic nerves, and this may be important for the increased heat production of sheep during cold exposure.