Silver nanoparticles of 10 nm diameter stabilised by poly(acrylic acid) were cast into films on ITO glass using the layer-by-laver assembly method with poly(diallyldimethylammonium chloride) as the cationic binding polymer. The films displayed strong surface plasmon band absorption and negligible light scattering. Application of a cathodic potential to the films resulted in a blue-shift in the position of the surface plasmon band. The rate of spectral shift was slow. taking from seconds to minutes, and was limited by ion diffusion into the film from solution. The shifts are attributed to the increased plasma frequency of the metal due to the excess, stored electrons.