A fluorescence method is presented for measuring the concentration of TEMPO-terminated chains in polystyrene samples prepared by controlled free radical polymerization. Exchange of TEMPO with a naphthoyloxy derivative is used to fluorescence-label those alkoxyamine-terminated polymer chains that are capable of further styrene addition, Determination of the fluorophore concentration in the exchanged polymer provides an accurate assessment of the concentration of alkoxyamine-terminated chains within a given sample. Fractionation of samples by gel permeation chromatography and simultaneous analysis by differential refractive index and fluorescence provides a measure of the distribution of nitroxyl-terminated chain ends as a function of molecular weight. This method is demonstrated on a series of polystyrene samples synthesized under various polymerization conditions.