A new method for the determination of triplet quantum yields, QT, based on the ketonization of ethyl acetoacetate (EAA) sensitized by triplet energy transfer, is described. Steady state and fluorescence measurements were carried out, using benzene, toluene, and p-xylene as energy donors. The QT values obtained by this simple method are in very good agreement with data obtained by other methods. A probable mechanism for photoketonization is discussed.