The population of valence-band electronic states of fullerene peapods (C-60@SWCNT) was tuned electrochemically in acetonitrile solutions. Electrochemistry of peapods was dominated by their capacitive charging without distinct faradaic processes. In situ Vis-NIR spectra of peapods showed similar features as those of empty nanotubes. Electrochemical charging caused reversible bleaching of the transitions between Van Hove singularities. This bleaching was mirrored by quenching of resonance Raman spectra of the tube-related modes. The A(g)(2) mode of C-60 exhibits considerable intensity increase upon anodic doping of peapods, but this mode is not enhanced at cathodic charging. (C) 2002 Elsevier Science B.V. All rights reserved.