Ideally, when a marker is used to determine the dominant diffusing species during phase formation, the marker should be chemically inert with respect to its surroundings, should not interfere significantly with the overall development of the reaction, and should not selectively couple to the diffusing motion of either element involved in the reaction. Finding a single marker that satisfies all these requirements is unfortunately extremely difficult and, in general, compromises have to be made. d’Heurle and Zang point out certain deficiencies tantalum has when used as a marker during CoSi2 formation. We acknowledge these deficiencies, but contend that the additional experiments carried out using tantalum markers in different systems (Ta marker in NiSi2) and different markers for the same system (Xe marker for CoSi2) suggest that these deficiencies are unlikely to make results of the original investigation completely invalid.