Condensation of benzene, anisole and N,N-dimethylaniline with benzaldehyde has been carried out in the presence of a USY zeolite (Si/Al 1.7.5). A combined study of the product distribution present in the liquid phase (di- and triarylmethanes together with N-benzylated byproducts in the case of dimethylaniline) as well as the organic material entrapped inside the zeolite micropores (triphenylmethane or trityl ions) has established that there is a direct relationship between the reactivity of the arene and the conversion of benzaldehyde, percentage of diarylmethanes in the liquid phase and population of trityl cations. A hydride transfer from triarylmethanes to diarylmethyl cation intermediates has been proposed as a key step for the simultaneous presence of trityl cations adsorbed in the solid and diarylmethanes in the liquid phase.