In this article, the Lattice Cluster Theory developed by Freed and coworkers is applied to the poly(styrene)/poly(vinyl methylether) system by measuring the enthalpy and the volume variation associated with the mixing of the two homopolymers. It comes out that the chains architectures previously chosen for the two macromolecules based on the phase diagram and of the partition function developed by the theory correctly predicts the sign of both Delta H-M and Delta V-M. The foreseen trends as function of mixture composition fit the experimental data only for Delta V-M; Delta H-M is higher than predicted, asymmetrical and independent on the chain lengths of the components. The conclusion is that the theory needs some final touches in order to obtain a better agreement with experiments. (C) 2008 Wiley Periodicals, Inc.