Solutions of transition metal cluster compounds were atomised by electrohydrodynamic means and the resultant aerosol was reacted with ethyne in the gas phase to catalyse the formation of carbon nanotubes. The use of an aerosol of iron pentacarbonyl resulted in the formation of multi-walled nanotubes, mostly 6-9 nm in diameter, whereas the use of iron dodecacarbonyl gave results that were concentration dependent. High concentrations resulted in a wide diameter range (30-200 nm) whereas lower concentrations gave multi-walled nanotubes with diameters of 19-23 nm. (C) 2003 Elsevier B.V. All rights reserved.