The formation of micelles of Pluronic block copolymers in poly(ethylene glycol) (PEG) was studied using fluorescence, solubilization measurements, and frozen fracture electron microscopy (FFEM) methods at 40 degrees C. It was discovered that surfactants L44 (EO10PO23EO10), P85 (EO26PO40EO26), and P105 (EO37PO56-EO37) can form micelles in PEG 200 (PEG with a nominal molecular weight of 200), and the critical micellization concentration (CIVIC) decreases with increasing molecular weight of the surfactants. The size of the micelles formed by these Pluronic block copolymers is in the range of 6-35 nm. The CIVIC values in PEG 200 are higher than those in aqueous solutions. (C) 2008 Elsevier Inc. All rights reserved.