When mammals are exposed to a cold environment for a long time, the capacity of nonshivering thermogenesis by brown adipose tissue (BAT) increases in association with the increased expression of some specific proteins and tissue hyperplasia, which are totally dependent on sympathetic innervation to this tissue. To clarify roles of the beta-adrenergic mechanism in BAT hyperplasia, the effects of chronic administration of various beta-adrenergic agonists on BAT were examined in rats, especially focusing on some agonists to the beta 3-adrenoceptor which is present specifically in adipocytes. Chronic administration of noradrenaline or isoproterenol for 7-10 days produced a marked increase in the tissue contents of DNA, total protein, mitochondrial uncoupling protein, and insulin-regulatable glucose transporter protein. The trophic effects of noradrenaline and isoproterenol were mimicked by chronic administration of beta 3-adrenergic agonists, such as CL316,243, BRL 26830A, and ICI D7114. These results suggest that the beta 3-adrenoceptor plays important roles for hyperplasia of BAT, and thereby increasing in the capacity of thermogenesis.