Turbulent drag reduction in a rotating disk apparatus was characterized for a homologous series of polyethylene oxide(PEO) polymers covering a wide range of molecular weights. The concentration dependence of drag reduction in this system was shown to obey an empirical dray reduction equation which had been previously established by Virk et al. for flows in capillary tubes. The linear correlation between polymer concentration and C/DR for different molecular weights of PEO was also obtained. In addition, [C], defined as a characteristic intrinsic concentration, was found to be extremely useful in normalizing the drag reduction data in one homologous series of PEO.