Many applications of ultrathin films require knowledge of the transport of molecules or ions through these films. In the case of films made of polyelectrolytes this may be a very interesting property since the polymer network may entrap large molecules but be penetrable to small ones. In order to obtain information on transport processes, the time dependence of the fluorescence of a dye (FITC) attached to a polymer and embedded in a defined, variable depth inside the film was studied by total internal reflection fluorescence. Adding a rhodamine solution to the outer aqueous phase, FITC quenching due to energy transfer was observed. From this the surface concentration and permeability of rhodamine was determined. We derive a depth-dependent diffusion coefficient of the order of 10(-15) cm(2) s(-1). Studying the paramagnetic quenching by the spin label 2,2,6,6,-tetramethyl-4-piperidinol-1-oxide the diffusion coefficient is at least two orders of magnitude larger for this smaller molecule.