A high molecular weight sample of anionically prepared polystyrene has been labelled specifically at the chain ends with nitroxide radicals. Line width analysis of the e.s.r. spectra of dilute solutions of the polymer gave rotational correlation times of the chain ends. The solvents used were toluene, α-chloronaphthalene and cyclohexane. After making allowance for the viscous drag of the solvent energy barriers to rotation were obtained and compared with those found previously for the random segmentally labelled polymer. Differences have been shown to arise through the internal barrier to rotation rather than through the pre-exponential term. It was found possible to show that the rotational mobility of the nitroxide was strictly governed by the mobility of the polymer chain end since the correlation time for rotation about the polymer—label bond was never less than 4τc, where τc is the observed correlation time for rotational diffusion of the nitroxide.