Time and q resolved light scattering and nuclear magnetic resonance spin-lattice relaxation time have been performed on polystyrene/poly(vinyl methyl ether) blends during the early stage of the spinodal decomposition. The two techniques are used to determine the apparent diffusion coefficient at two different temperatures. A satisfying agreement is found between the results of T-1 n.m.r. measurements and those from light scattering. Otherwise, it has been shown that n.m.r. spin-lattice relaxation measurements, during the decomposition time, permits discrimination between spinodal decomposition and nucleation and growth. T-1 rho experiments indicate that the homogeneous phase as well as the phase-separated quenched blend contain short scale inhomogeneities but it is not clear whether they compete with the larger scale spinodal decomposition process. (C) 1997 Elsevier Science Ltd.