The phase behaviour of blends of glycidyl methacrylate/methyl methacrylate (GMA/MMA) copolymers with styrene/acrylonitrile (SAN) copolymers and of GMA/styrene copolymers with tetramethyl polycarbonate and poly(2,6-dimethyl-1,4-phenylene oxide) has been determined and analysed using two theoretical approaches. Binary interaction densities for repeat-unit pairs were evaluated from the lower critical solution temperature type phase behaviour using the lattice-fluid theory of Sanchez and Lacombe and from copolymer composition miscibility boundaries using the Flory-Huggins theory. For the GMA/MMA-SAN system the interaction energies obtained by the two approaches agree quite well with each other and with independent information obtained by the critical molecular-weight method.