Diffusion has a significant effect in zeolite catalysis. Molecular traffic control is a good example. For the study of diffusion in microporous crystalline materials with 10 MR/12 MR interconnected channels, as H-CIT-1, the isomers, para- and ortho-xylene are excellent probes. In this regard, by means of a FTIR technique, codiffusion and counterdiffusion of these isomers were studied. The values of the diffusivities in the codiffusion and counterdiffusion experiments were measured. A correlation in the transport of both isomers, during codiffusion and counterdiffusion was observed. Throughout codiffusion, the more mobile p-xylene molecule hinders the motion of o-xylene. During the counterdiffusion case, when p-xylene diffuses "in" and o-xylene "out" the zeolite, the 10 MR channels, which are blocked for the o-xylene molecules, are free for p-xylene motion. Subsequently, under the experimental conditions of the present study, molecular traffic control, takes place. (C) 2009 Elsevier B.V. All rights reserved.