Discontinuous W films have been used as diffusion markers to study interdiffusion during the sequential formation of CuAl2, CuAl and Cu9Al4 intermetallic compounds in bimetallic Al and Cu thin films. Rutherford backscattering spectroscopy has been used to determine marker displacement. For the formation of CuAl2 between Cu and Al, both diffuse. For the formation of CuAl between Cu and CuAl2, Cu is the dominant diffusing species. However, for the formation of Cu9Al4 between Cu and CuAl, again both Cu and Al diffuse.