The nitrophorins are ferriheme proteins that are present in the saliva of two species of the blood-sucking insects, the kissing bug (Rhodnius prolixus) and the bedbug (Cimex lectularius). These proteins provide a means of stabilizing NO for long periods of time in the insect salivary glands, and are responsible for transporting NO to the tissues of the victim. The NO is reversibly bound to a ferric heme with binding constants in the micromolar to nanomolar range, which upon injection of the saliva into the tissues of the victim the NO dissociates causing vasodilation and inhibition of platelet aggregation. The stabilization of the ferric NO heme center and preservation of reversible binding constants that facilitate these proteins NO storage and transportation functions will be discussed.