Static and dynamic light scattering were measured for monodisperse poly(ethylene oxide) (PEG) in water and methanol at 25 degrees C. PEOs of three different molecular weights ranging from nominal M(w), = 2.6 x 10(4) to 9.96 x 10(5) were used. For all of these molecular weights, angular dependence of Zimm plots showed no downturn at low angles not only in water but also in methanol, indicating no large aggregates of PEO in both solvents. Furthermore, apparent weight-average molecular weight M(w,app), radius of gyration R(G,app), and hydrodynamic radius R(H,app) did not change over 3 weeks. This observation indicates that molecularly dispersed PEO is stable and aggregate-free property is inherent in these solvents.