The tracer diffusion of deuterated polystyrene (dPS) into natural polystyrene-poly(alpha-methyl styrene) (hPS-P alpha MS) blends has been studied as well as the diffusion of dPS-P alpha MS blends into hPS-P alpha MS blends. Nuclear reaction analysis (NRA) as a depth profiling technique is shown to be useful to study the different systems. The diffusion constants have been determined as a function of temperature and as a function of composition of the blend of the tracer and the matrix. Blends as a tracer shaw a strong enhancement in diffusion in comparison to the pure dPS tracer, indicating that the intradiffusion coefficient measured in a sample where there is no chemical gradient is much bigger than the tracer diffusion measured from a thin film of pure dPS. The glass transition temperature T-g has a considerable influence on the diffusion.