Xenon has been used as a structural probe of solid poly(ethylene oxide)/atactic poly(methyl methacrylate) (PEO/PMMA) blends of concentrations 10/90 to 75/25. Xe-129-NMR spectra at 293 K show significant changes in line width and chemical shift as the blend composition is varied. The Xe-129 spectra are interpreted in terms of exchange between amorphous single-phase PEO and PMMA domains. It is shown that a simple two-site exchange model can be used to calculate spectra which fit the experimental data over the whole concentration range. Xe exchange between blend subregions is demonstrated also by a two-dimensional NMR experiment. The PEO/PMMA results are compared to previously published poly(vinylidene fluoride)/PMMA Xe-129 spectra.