Changes in the plasma free fatty acids of a pancreatectomized subject and in free fatty acids and insulin in 10 normal subjects in response to the in vivo infusion of epinephrine alone, epinephrine plus phentolamine, and epinephrine plus propranolol indicate that both alpha and beta adrenergic receptors are present in human adipose tissue. Under the experimental conditions used, adipose tissue appeared to be more responsive to epinephrine than did the cardiovascular system.