A procedure has been developed for determining the concentrations of superoxide anion radical (SOAR) in aprotonic fluids by using semiconductor chemical sensors. SOAR life in pure solutions is 6.3 hours. Supplements of biological fluids (blood, urine, plasma) increase the rate of SOAR death. There is a great difference in the reaction rate of SOAR with biological fluids in apparently healthy and ill individuals. It is suggested that the above procedure opens vistas both for studies of vital activity and for diagnosis of abnormalities.