MARY and Optically Detected ESR techniques were used to infer that radical cation and radical anion of biphenyl in concentrated hexane solutions have substantially different second moments of their ESR spectra. This observation is interpreted in terms of different types of processes between the two radical ions and the neutral parent molecule. It is suggested that dimerization is prevalent for biphenyl radical cation, while biphenyl radical anion is rather involved in fast ion-molecular charge transfer reaction. (c) 2005 Elsevier B.V. All rights reserved.