Nitric oxide (NO�), generated by the catalytic action of nitric oxide synthase on L-arginine (1 ,2 ), regulates vascular tone, augments cell-cell communications, and governs many intracellular events (3 –8 ). Further, NO� plays a critical role in host immunity, particularly effective against a number of intracellular pathogens (9 –11 ). There are two distinct classes of nitric oxide synthases, constitutive and inducible (12 ), the latter of which is found in phagocytic cells (13 ) and can be induced in other cells by exposure to endotoxins and/or cytokines (14 ); see Note 1 .