The influence of certain stabilizers on the aerobic photobleaching of buffered riboflavin phosphate solutions exuosed to fluorescent 1 ight was investigated. Disodium ethylenediamine (EDTA) demonstrated the greatest stabilizing effect followed by thiourea, methyl paraben, DL-methionine and sodium thiosul fate. The photostabilizing effect of these agents increased as their concentrations increased. Other stabilizers enhanced the photostability of riboflavin solutions with lesser and varying degrees. fluence the rate of photodegradation o f riboflavin solutions in the presence or absence of EDTA.The pH and buffer species o f the solutions appeared to in-*