Using molten urea as the solvent, single walled carbon nanotubes (SWCNTs) are dispersed and functionalized with arenediazonium salts in less than 15 min to afford predominantly unbundled functionalized SWCNTs. This technique provides a rapid and economically viable route to produce covalently functionalized nanotubes in large amounts with an industrially friendly method. (C) 2009 Elsevier Ltd. All rights reserved.