Abstract: A method for prophylaxis of treatment of an animal for systemic hypotension induced by internal nitrogen oxide production. The method involves administering a therapeutically effective amount of certain arginine derivatives to inhibit nitrogen oxide formation from arginine. Preferaby N.sup.G -substituted arginine or an N.sup.G,N.sup.G -disubstituted arginine (having at least one hydrogen on a terminal guanidino amino group replaced by another atomic species) is administered to an animal possibly developing or already having induced systemic hypotension. The arginine derivatives are preferably of the L configuration and include pharmaceutically acceptable addition salts. Prophylaxis or treatment or systemic hypotension in a patient which has been induced by chemotherapeutic treatment with biologic response modifiers such as tumor necrosis factor or interleukin-2 may be accomplished. Treatment of an animal for systemic hypotension induced by endotoxin, i.e.