A method for producing aligned carbon nanotubes and/or nanofibres comprises providing finely divided substrate particle having substantially smooth faces with radii of curvature of more than 1 μm and of length and breadth between 1 μm and 5 mm and having catalyst material on their surface and a carbon-containing gas at a temperature and pressure at which the carbon-containing gas will react to form carbon when in the presence of the supported catalyst, and forming aligned nanotubes and/or nanofibres by the carbon-forming reaction.