We propose an idea for the chirality-selective growth of nanotubes by controlling the type of caps that form on the catalyst at the nucleation stage. Particular caps could be favored by their epitaxial relationship to the solid catalyst surface and the corresponding tubes grow preferentially. We show by ab initio calculations that lattice-matched caps and tubes are more stable next to a Ni surface than non-lattice-matched structures. This explains the dominance of certain chiralities in samples grown by low-temperature chemical vapor deposition. (c) 2006 Elsevier B.V. All rights reserved.