Diffusion is considered important in the process of mixing old and new binders during asphalt recycling. The degree of mixing is presumed to greatly influence the final properties of recycled asphalt concrete. Previously, studies have been undertaken to investigate diffusion using FTIR-ATR (Fourier Transform Infrared Spectroscopy using Attenuated Total Reflectance). A need was identified to verify, if the rates of diffusion detected using FTIR-ATR were accompanied by changes in rheological properties. In this paper, a dynamic shear rheometer (DSR) with parallel plates is used for monitoring diffusion. Diffusion coefficients obtained at 60, 80 and 100 degrees C from tests of a soft bitumen (rejuvenator) diffusing into a stiff one are presented. The diffusion coefficients determined are compared with the corresponding diffusion coefficients obtained using FTIR-ATR. The comparison shows that the rates of diffusion detected by the DSR are of the same magnitude, but somewhat higher than the ones detected by FTIR-ATR.