The rheological response of high molecular weight tracer chains of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA), separately blended with low molecular weight PEO/PMMA matrices of varying composition, were obtained over a 120 deg temperature window. Monomer friction factors, ζ, for each component as a function of temperature and matrix composition were extracted by various means, all of which yielded consistent results. The tracer diffusivities of low molecular weight PEO chains in some of the same blends were obtained by forced Rayleigh scattering, and the resulting friction factors agree well with those obtained using rheology. The overall results show that the mobilities of both PMMA and PEO are strongly composition-dependent in PMMA-rich blends, their monomeric friction factors dropping precipitously upon addition of small amounts of PEO. The composition dependence of the PMMA ζ is strong over a wide composition range, whereas that of PEO is only significant at high PMMA content blends. Friction factors for the PEO component are significantly larger than those inferred from segmental dynamics measurements reported in the literature. The Lodge-McLeish self-concentration model, as usually applied, is unable to predict the observed behavior of either component. However, the data can be nearly quantitatively described using a simple but empirical mixing rule. Selected experiments were repeated using a PEO matrix with methoxyl rather than hydroxyl end groups; except for the change in glass transition temperature for the PEO, no significant effects were observed.