The influence of androgen status on the regulation of lipolysis and number of beta-adrenoceptors in isolated adipocytes was studied in male rats. Castration resulted in decreased catecholamine-induced as well as forskolin-induced lipolysis. beta-adrenoceptor number, examined by a whole cell cyanopindolol binding assay, was also diminished to a similar extent. Testosterone treatment of castrated rats normalized lipolysis as well as beta-adrenoceptor number. These results demonstrate that testosterone stimulates catecholamine-induced lipolysis in vivo by increasing the number of beta-adrenoceptors as well as the activity of adenylate cyclase, confirming previous in vitro studies performed in adipose precursor cells.