1. Hemolysis may be produced by previously irradiated fluorescein, eosine and erythrosine. 2. Similarly, previously irradiated fluorescein, eosine and erythrosine oxidize iodide ion. 3. These findings render untenable the sensitization theory of Tappeiner and other theories which necessitate the simultaneous action of light and the photodynamic substance, while supporting Straub's theory of direct oxidation of cell constituents. 4. Oxidation must be considered as a probable underlying cause in photodynamic hemolysis and all other photodynamic phenomena.