We report a study of the local dynamics in polyisobutylene (PIB) melts using quasi-elastic neutron scattering (QENS). QENS measurements were carried out on the high resolution back-scattering spectrometer IRIS (ISIS) in the temperature range 300-460 K. The QENS data were analysed in the time domain, in order to extract information on the a-process in PIB. We show that time-temperature superposition is obeyed. The temperature dependence of the shift factors derived by QENS is in good agreement with 13C NMR and ESR literature data. However, the temperature dependence of the molecular motion observed by QENS differs considerably from the one determined from viscosity and neutron spin echo measurements. © 2002 Published by Elsevier Science B.V.