The reinterpretation of our data by Shi and Davis [Catal. Today 58 (2000) 255] raises some questions concerning the precise mechanism by which an ethene probe initiates the Fischer-Tropsch reaction. However, the experimental data are firmly based and it is clear that our original proposal still stands, namely, that the most probable low energy pathway for the formation of hydrocarbons in the Fischer-Tropsch reaction involves the polymerisation of surface methylene, initiated by a surface vinyl and propagated by surface alkenyl species. (C) 2001 Published by Elsevier Science B.V.