Electrochemical measurements were performed on a carbon nanotube mat as a working electrode using different salt solutions. The gravimetric capacitance of the nanotube material was estimated and its effective surface area was determined in a purely electrochemical way. We also studied the Raman response upon electrochemical p-doping of carbon nanotubes. The frequency shifts and the Raman intensities of the radial breathing mode and the high-energy stretching-like mode were examined as a function of doping level. (C) 2003 Elsevier Science B.V. All rights reserved.