Four methods for detecting cocontinuity in a poly(ethylene oxide)/polystyrene (PEO/PS) system are compared: scanning electron microscopy (SEM) with image analysis, solvent extraction, electrical conductivity measurements, and rheological measurements. Measurements of the amounts of interfacial area using a novel image analysis method showed that the interfacial area reached local maxima at the boundaries of the region of cocontinuity. Solvent extraction experiments allowed the region of cocontinuity to be characterized based on the ability of the blends to maintain their shape during extraction and measurements of the degree of continuity of the PEO phase. Electrical conductivity measurements were modeled using percolation theory to estimate the minimum PEO concentration required to form a continuous phase. Rheological measurements showed that the elastic modulus measured at low frequencies reached local maxima at the boundaries of the region of cocontinuity. SEM with image analysis and solvent extraction provide the most quantitative information about the blend morphology and are the most powerful methods for characterizing the region of cocontinuity. (C) 2004 Society of Plastics Engineers.