High resolution photoemission spectroscopy was used to follow the modification of the electronic properties of single wall carbon nanotubes determined by the interaction with adsorbed electron donor and acceptor species. Valence band, C1s and adsorbate core level spectra were monitored to reveal the adsorption and to follow the Fermi level shift induced by the charge exchange between C lattice and dopants. In the presence of nitrogen dioxide, a considerable charge withdrawal from C atoms takes place, which is revealed by the binding energy shift of the C1s peak. On the contrary, adsorbed H2O does not appear to interact with nanotubes. For Li doping, the occurrence of an efficient electron injection into the tube structure is demonstrated by the evidence of Li ionisation, by the enhancement of the density of states near the Fermi level and by the partial conduction band filling, which originates a rigid shift of all C spectral structures. (c) 2005 Elsevier B.V. All rights reserved.