Nitric oxide (NO) is receiving interest because of its use in patients with acute respiratory distress syndrome. Because more studies are being conducted, researchers are discovering a vast array of physiological effects attributable to NO. NO has been implicated as having a role in the endogenous regulation of blood pressure; smooth, skeletal, and cardiac muscle relaxation; renal and immune system functioning; and selective pulmonary vasodilation. This article looks at the pharmacological and physiological effects of NO and its current use in the clinical setting.