Measurement of the amount of nitric oxide (NO), the free radical oxide of nitrogen which functions in various physiological capacities including as a vasodilator, signaling molecule, neurotransmitter and microbicide, in a specified volume of fluid which has escaped from blood vessels and been deposited within tissues or on tissue surfaces as a result of inflammation, a usually localized, protective reaction of tissue to irritation, injury or infection, characterized by pain, redness, swelling and sometimes loss of function.