We studied the effects of a nitric oxide synthase (NOS) inhibitor, N [omega]-nitro-l-arginine-methyl ester (l-NAME), on cardiac depression and bronchospasm provoked by systemic anaphylaxis in vivo in rabbits. Animals pretreated with l-NAME showed lower survival rates than control animals pretreated with normal saline. The survival rate in l-NAME-pretreated animals was increased by the administration of l-arginine after initiation of anaphylaxis. Cardiac output fell significantly in animals pretreated with l-NAME compared with controls, although venous return was increased. In animals pretreated with l-NAME, pulmonary resistance was significantly increased, and administration of arginine attenuated the bronchospasm. In conclusion, these results, along with the low survival rates in the l-NAME-treated animals, suggest that NO production may be beneficial to cardiac depression and bronchospasm in anaphylaxis in vivo.