The diffusion of various molecular weight poly (ethyleneglycol)s (PEG) confined between the lamellae of magnetically aligned bicelles has been measured using stimulated echo (STE) pulsed field gradient (PFG) H-1 nuclear magnetic resonance (NMR) spectroscopy. Bicelles were formulated to contain dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidylglycerol (DMPG), and dihexanoylphosphatidylcholine (DHPC) in the proportion DMPG/DMPC = 0.05 and q = (DMPC + DMPG)/DHPC = 4.5. PEG diffusion within the interlamellar spaces between such bicelles was found to be unrestricted over diffusion distances of tens of microns. Two confinement regimes could be differentiated according to the dependence of the reduced PEG diffusivity D/D-0, where D-0 is the unconfined PEG diffusion coefficient. on the relative confinement R-h/H, where R-h is the unperturbed hydration radius of the particular PEG and H approximate to 60 A is the separation between apposing lamellae of the magnetically aligned bicelles. In the regime R-h/H < 0.4. the reduced PEG diffusivity was altered only in proportion to the viscosity increase associated with the bicelle dispersion relative to bulk solution. In the regime R-h/H > 0.4, the reduced PEG diffusivity scaled as (R-h/H)(-2/3), in agreement with scaling theories for confined polymers.