A simple analysis of marker motion in a single compound layer is presented. The compound layer may either act as a transport layer with invariant thickness, as in the case of solid-phase epitaxial growth of amorphous silicon through a thin-film Pd2Si layer on crystalline silicon, or the compound layer may grow itself as in a planar binary diffusion couple. The analysis takes into account possibe volume changes during compound formation and holds for interface-controlled as well as for diffusion-controlled growth of the compound layer. Reanalysis of marker motion data in Ni2Si in Ni/Si thin-film diffusion couple shows that the ratio DNi/D Si of the diffusivities of Ni (DNi) and Si (D Si) in Ni2Si at 325°C is at least about ten times larger than that evaluated previously. Marker motion data for the growth of Cu6Sn5 at room temperature in a bimetallic Cu/Sn thin-film diffusion couple are presented and analyzed.