The pharmacological effects of FAD on the heart, peripheral blood vessels, arterial pressure, and intestinal canal were observed on rabbits and the results were compared with those of adenylic acid and FMN. FAD has a marked depressive action on the blood pressure, an inhibitory action the movements of the intestinal canal, a constrictive action on the ear blood vessels, and an inhibitory action on the heart beat of the rabbit. These pharmacological actions of FAD are mainly ascribable to its adenylic acid component, and through the combination with FMN these actions are strengthened and prolonged.