A method and composition to inhibit the enzyme nitric oxide dioxygenase (NOD) and therefore accumulate nitric oxide (NO) in cells or tissues. By preventing NO removal, the inhibitors may effect cellular signaling, modulate vasotension, enhance O.sub.2 delivery to tissues, and provide antibiotic and/or antineoplastic effects. Inhibitors include compounds that bind to the iron in the heme portion of NOD, and include allicin and azoles.