The Kirkendall effect-induced migration of inert markers during a diffusion-controlled growth of Co¯Si intermetallics was studied at 1100°C. It is demonstrated experimentally that more than one Kirkendall marker plane can appear within the newly formed Co-silicide layers. It is also shown that, under specific conditions, a marker plane cannot develop at all in any of the product phases. The marker behaviour is discussed in terms of the velocity of the Kirkendall frame of reference relative to the laboratory-fixed (Matano) frame. A phenomenological approach is presented to predict the number and positions of the Kirkendall marker planes developing in a multiphase diffusion zone.