Pharmacological properties of adrenergic receptors have been investigated in fat cells isolated from omental adipose tissue of the Dog. From the results, the following points can be stated. 1. Lipolysis is markedly enhanced by isoproterenol. This effect is competitively inhibited by propranolol (a beta-adrenoceptor blocking agent). (Fig 1). 2. The beta 2-sympathomimetic salbutamol is found to have only a slight effect on lipolysis rate (Fig. 2). 3. The epinephrine-induced lipolysis is potentiated by phentolamine (an alpha-adrenoceptor blocking agent) only on large sized adipose cells (mean fat cell size 96.7 +/- 5.3 micrometer; Fig. 5). 4. The isoproterenol-induced lipolysis is partially inhibited by phenylephrine (an alpha-adrenomimetic drug) (Table I). These findings show that beta 1 nature of the receptors involved in the adrenergic control of lipolysis in Dog adipose tissue. Moreover an antilipolytic effect of epinephrine, via alpha-adrenergic receptors, is observed, especially in large adipose cells.