Abstract: A method of assessing certain disease conditions of body tissues and body fluids by the measurement of hydroperoxides therein; includes using the enzyme prostaglandin H synthase and observing the rate of enzyme-catalyzed oxygenation reaction, preferably with equipment such as a polarographic oxygen electrode that monitors the oxygen concentration. The presence of increased amounts of hydroperoxide cause a faster attainment of the optimal rate of enzyme-catalyzed oxygen consumption. This enzymic assay provides high sensitivity and selectivity for hydroperoxides. Cyanide may also be introduced to temper the reaction velocity to facilitate monitoring the enzyme reaction.