Aligned multiwall carbon nanotubes were grown on thermally oxidized silicon, quartz, and sapphire substrates without a predeposition of a catalyst. They were grown by chemical vapor deposition at 980?C with benzene as precursor and ferrocene as catalyst and had a length of several tens of microns. It was found that the order in which the precursor and catalyst were introduced during chemical vapor deposition determines the orientation of the nanotubes. Surface elemental analysis shows that the presence of catalyst particles on the substrate is essential for their vertical alignment. Transmission electron microscopy shows that the iron particles are embedded inside the nanotubes.