The rebuttal by Maitlis and Turner does not address the basis of our reinterpretation of the data generated by Maitlis and coworkers using C-13-labeled ethene. Maitlis and coworkers considered that the C-13/C-12 ratio in the surface species decreased with carbon number and we indicated that this was not possible. We reinterpreted their data, using only the C-13-containing components. Because of the agreement between their experimental results and the expectations of a decrease in the C-13 content of products of increasing carbon number that was based on their incorrect theoretical interpretation of the isotopic content of surface species, Maitlis and coworkers concluded that ethene initiates chain growth with the formation of a surface bound vinyl intermediate. Our correct interpretation of their experimental data shows that ethene functions to initiate chain growth, and has been advanced previously by several investigators. The C-13-data and other isotopic tracer data, in our view, do not provide direct evidence to favor a surface bound vinyl intermediate over other possible surface species. In their rebuttal, Maitlis and Turner involve new issues, including the view that the addition of ethene alters the alpha -value for the synthesis, and a few of these issues are addressed. (C) 2001 Published by Elsevier Science B.V.