Noradrenaline (NA) administered systemically or into the lateral cerebral ventricle (ICV) in appropriate doses increased heat production and colonic temperature in 1-12 day-old guinea pigs. The effect of systemically applied NA could be blocked by systemically applied beta-adrenergic receptor blockers, while beta-blockers administered centrally or alpha-adrenergic blockers injected systemically or centrally had no effect on the action of systemically applied NA. Accordingly, the effect of systemically applied NA was mediated by peripheral beta-adrenergic receptors. The effect of centrally applied NA was blocked by alpha-adrenergic receptor antagonists applied into the lateral cerebral ventricle and attenuated by systemically applied phentolamine, but not by phenoxybenzamine or ergotamine. Beta-adrenergic receptor blocking agents applied either ICV or systemically had no effect on the action of centrally applied NA. It is concluded that ICV applied NA acts through central alpha-adrenergic receptors.