The formation of well-defined colloidal particles (mesoglobules) from the thermosensitive polymer poly(methoxydiethyleneglycol methacrylate) was observed in dilute aqueous solutions (0.5-1.0 g/L) by turbidimetry and dynamic light scattering (DLS). DLS measurements were performed at 70 A degrees C and showed a strong influence of polymer molecular weight: the hydrodynamic diameters of the mesoglobules increased from ca. 160 to 330 nm with a relatively small, i.e., from 6,400 to 14,000, increase in molecular weight. The addition of sodium dodecyl sulfate (SDS) at surfactant/polymer ratios (s/p, g/g) ranging from 0.3 to 0.5 practically inhibited the clouding of the solutions as the initial transmittance decreased by only 10-30%. Furthermore, a dramatic shift of the original cloud point values taken as a 10% decrease in transmittance, by approximately 20-60 A degrees C was registered upon the surfactant addition. The presence of SDS resulted in size reduction by 52-90% as indicated by DLS.