The rotating-frame spin-lattice relaxation time for protons, T-1p,(H-1), was measured indirectly from C-13 CP/MAS/DD NMR to probe possible molecular scales of heterogeneity in the miscible poly(benzyl methacrylate) (PBzMA)/poly(ethylene oxide) (PEO) blend over the whole composition range. According to the NMR results, only one phase was observed for the blends in which the PEO component is less than 16% (w/w). This miscible amorphous phase with PBzMA and PEO chains was mixed at the molecular level. Three phases were detected for the blends with PEO component >16%, containing one miscible homogenous PBzMA-rich phase, one constrained PEO phase and one crystalline PEO phase. The PEO component asymptotically increases in the miscible homogenous PBzMA-rich phase as the PEO composition increases. NMR analysis helped resolve the complex phase domains in the PBzMA/PEO blend that is composed of an amorphous mixture of PBzMA/PEO and crystalline PEO spherulite regions. The intra- and inter-lamellar domains in the PEO spherulites are influenced and complicated by the surrounding amorphous PBzMA/PEO mixture with varying composition. (C) 2001 Elsevier Science Ltd. All rights reserved.