We have used variable-temperature solid-state NMR methods to determine that amorphous polypropylene (a-PP) is miscible with blends of poly(ethylene)ethylethylene (PEE) and poly(ethylene-co-octadecene) (PE-OD). Rothwell-Waugh Line-broadening effects and selective H-1 T-1 rho measurements indicate that the frequency of reorientational chain dynamics increases for a-PP upon blending with PEE and PE-OD but remains unchanged for blends with poly(ethylene-co-dodecene) (PE-DD). We infer partial miscibility on the basis of converged but incompletely averaged relaxation curves for the a-PP/PEE and a-PP/PE-OD blends; while the a-PP/PE-DD blends were found to be immiscible. Dipolar filter experiments in which spin-diffusion was used to monitor polarization transfer provided direct evidence for miscibility in the a-PP/PE-OD blends and immiscibility in the a-PP/PE-DD blends. From these data, domain sizes were calculated to be 5.1 nm (i.e., on the order of chain dimensions) for the miscible regions of the PPI PE-OD blend.