Hybrid polymer/lipid giant unilamellar vesicles (GUVs) were developed using lipids of respectively low and high melting transition temperature (DPPC: 1,2-dipalmitoyl-sn-glycero-3 phosphocholine, T-m = 41 degrees C, and POPC: palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine; T-m = -2 degrees C) and a copolymer poly(dimethylsiloxane)-graft-poly(ethylene oxide) (PDMS-g-PEO) well known to self-assemble into vesicular structures. Using epifluorescence microscopy as well as differential scanning calorimetry (DSC), different structures have been identified depending on the molar composition and on the fluid or gel state of the lipid used. The most promising objects are hybrid vesicles with copolymer as the major component, in which lipids are either randomly distributed or present "raft-like'' domains in the polymer-rich membrane. The results are discussed on the basis of the fluidity of the different components and of their respective membrane thicknesses