Small-angle neutron scattering (SANS) was used to investigate the micellar structure formed by a poly(oxyethylene-oxypropylene-oxyethylene) (PEO(13)PPO(30)PEO(13), Pluronic L64) copolymer in D2O over a temperature range of 8.4-35.0 degrees C. The intermicellar interactions were corrected by using an equivalent hard sphere approximation with an equivalent hard sphere radius. The aggregation number of the micelles decreased with decreasing temperature. The micellar scattering behavior could be well described by a core-shell structure. Based on the core-shell model, the volume fraction of the polymer segments in the micellar shell. was less than 0.2. The micellar molar mass became larger after having introduced an organic solvent (xylene) into the system and increased with increasing amount of solubilized xylene. The maximum amount of solubilized xylene in the micelle was of the order of 0.3-0.4 xylene molecule per PO unit.