Studies of photosensitized oxidation of model biological systems are proposed. The role of singlet oxygen, superoxide ion, and other reactive intermediates in the oxidation of amino acids, enzymes and nuclear bases will be determined. The mechanism of protective action of carotenes, amines, and phenols will be studied using kinetic techniques, flash photolysis, and competitive inhibition with specific singlet oxygen and superoxide traps. Products will be determined. The chemistry of superoxide ion will be further elucidated, as will the chemistry of metal-oxygen complexes. Models for enzymic oxidations should be clarified by these studies, and a possible carcinogenesis mechanism can be tested.