Several chlorooxygen compounds, hydrogen peroxide and reducing molecules in the presence of chelated iron (Fenton systems) are oxidants of biological relevance. These compounds are either produced in living tissues or are in use as disinfectants or drugs. Tetrachlorodecaoxide as the active principle in the drug OXOFERIN can be differentiated from the above mentioned oxidants by means of simple biochemical test systems where different activators and detector molecules are used.