Thionine and toluidine blue were used as sentizers on photooxidation processes of methionine, tryosine and tryptophane. They were more effective than methylene blue. Methionine was photooxidized to sulfoxide and tryptophane to kinurenine. A tyrosine-sensitizer addition compound was postulated. Dye concentration, pH, temperature and EDTA presence conditions were determined on each one of the modification reactions. Methionine at acid pH was selectively modified. On the basis of obtained results and published references, a direct interaction of singlet oxygen with methionine and tryptophase and the excited dye with tyrosine was respectively discussed.