Diffusion data for amorphous binary alloys are scarce in the literature. There are no data available for the diffusion of Al in Al–Pt amorphous phase known to the authors. High-temperature successive deposition of components was used in the present experiments to reveal the elementary processes of reactive diffusion forming the metastable amorphous phase and to determine the diffusion coefficient of Al in this phase:D(&agr;)=(1.2±0.4)×10−10×exp[−(6.9±0.1)×104J&hthinsp;mol−1/RT]m2&hthinsp;s−1.This value, taken from thin film experiments, can be considered as a good approximation to the bulk diffusion coefficient. ©1998 American Institute of Physics.