The relative proportion of antilipolytic alpha-2 and lipolytic beta adrenoceptors and the adrenoceptors was studied in adipocytes from lean and obese dogs. The modification of the adrenergic status in the adipose tissue from obese dogs consists of an increase in alpha-2 adrenoceptor number (identified by [3H]yohimbine) and a decrease in beta adrenoceptor number (identified by [3H]dihydroalprenolol). Neither the number of beta adrenoceptors in the leukocytes nor the number of alpha-2 adrenoceptors in the platelets were altered in obesity. This predominance of alpha-2 adrenoceptors in adipocytes from obese dogs induced a reduction of the lipolytic efficacy of epinephrine (i.e., increase in the concentration able to induce half-maximal stimulation of lipolysis). Moreover, the number of beta adrenoceptors in the high-affinity state was increased in adipose tissue from obese dogs. It is concluded first that the striking modifications in the adrenergic status of the adipose tissue in obesity is specific to this tissue and secondly that the rise of the beta adrenoceptor in the high-affinity state could explain the fact that catecholamines remain lipolytic agents and that weight loss is increased by starvation in the obese dog.