Some cellulosic derivatives are soluble in cold water, but above a clouding temperature they form a polymer-rich phase which progressively expels water as the temperature is raised. This phase separation may be modified by adding surfactants. Over a certain range of compositions and temperatures, some of these systems form thermoreversible gels. Small angle neutron scattering experiments are reported for the gels made of ethyl hydroxyethyl cellulose (type CP-30) and cationic surfactants. The results show that the surfactants cause a dissociation of the polymer-rich phase into smaller lumps, with sizes on the order of 500 Angstrom. Each lump is formed by the loose association of polymer strands belonging to many macromolecules and is covered by surfactant. The mechanical rigidity of the gel originates from the association of the macromolecules through these lumps.