We present an efficient method to achieve high-purity boron doped single-walled carbon nanotubes (SWCNT) using an adapted substitution reaction. We observe that around 15 at.% of the carbon atoms are substituted by boron, with local concentrations of up to 20 at.% (higher than previous report). The as-prepared material was characterised by local scale method: transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) as well as by bulk sensitive methods like optical spectroscopy in the infrared energy range (IR), X-ray photoemission spectroscopy (XPS) and bulk sensitive high-resolution EELS. (C) 2003 Elsevier B.V. All rights reserved.