In ovalbumin-sensitized guinea pigs, the serum catecholamines were significantly increased 20 or 120 min after antigen injection. The highest serum cathecholamine values were obtained in animals which were selected during a severe state of protracted shock, and in those which died in protracted shock. Antihistamine pretreatment reduced the serum noradrenaline, but not the adrenaline values in anaphylaxis. In urethane anesthesia, the anaphylactic serum catecholamine levels (especially noradrenaline) were lower than in nonanesthetized animals. The adrenaline and noradrenaline content of the adrenals in protracted and in acute anaphylactic shock did not differ from control values.