The effects of noradrenaline (NA) injection (40 micrograms/100 g, i.p.) on plasma glucagon, corticosterone (CS), deoxycorticosterone (DOCS), glucose, and free fatty acids (FFA) were investigated in cold-acclimated rats (CA) and warm controls (WC). The CA were transferred to warm control temperature ca. 18 h prior to NA or saline injection. The animals were decapitated and the trunk blood was collected 0, 10, 20, and 40 min after the injection. Plasma glucagon level increased significantly during the experimental period after NA, while saline did not influence its level. The magnitude of increase as assessed by 95% confidence interval was significantly greater in CA than in WC. Plasma CS and DOCS were significantly increased by saline injection, but NA caused greater elevations of these steroid-hormones. The magnitudes of increases were also greater in CA. In contrast to the hormonal responses, NA-induced increases of plasma glucose and FFA levels were smaller in CA than in WC. These results suggest that glucagon and glucocorticoids are released, at least partly, by NA, and these thermogenic factors act in synergism, enhancing nonshivering thermogenesis through an accelerated utilization of energy substrates such as glucose and FFA.