We report a quasi-elastic neutron scattering (QENS) study of local dynamics in isotactic polypropylene (iPP) melts. QENS measurements were carried out on the spectrometer IRIS (ISIS, UK), using a series of selectively deuterated iPP samples. Analysis of the intermediate incoherent scattering functions was conducted using two different models: (a) a two-component model involving a fast process and conformational transitions and (b) a three-component model including methyl group reorientations. We show that consistent results between the selectively deuterated samples are only obtained when methyl group reorientations are explicitly taken into account. The results presented here are consistent with the simulated intermediate scattering functions of atactic polypropylene [Ahumada, O.; Theodorou, D. N.; Triolo, A.; Arrighi, V.; Karatasos, C.; Ryckaert, J.-P. Macromolecules 2002, 35, 7110] which revealed contributions from torsional transitions of the methyl groups and segmental motion, in addition to a fast process. © 2008 American Chemical Society.