Changes in the infrared spectra of poly(methyl methacrylate) as a function of temperature have been examined. The results presented here, together with a consideration of normal coordinate calculations reported in the literature. suggest that previous assignments of bands in the 1300-1050 cm(-1) region of the spectrum to specific conformations of the ester pendant group are incorrect. Certain bands in this and other regions of the spectrum are nevertheless very sensitive to temperature. It is proposed that this sensitivity is a function of both conformational effects and vibrational relaxation effects. The latter are usually neglected in vibrational spectroscopic studies of polymers, and it is proposed that more attention be paid to changes in band shapes when considering changes in the spectra of polymers as a function of temperature.