Stable gold nanoparticles have been prepared by the chemical reduction of tetrachloroaurate in the presence of PVP and the metallopolymer [Os(bpy)(2)(PVP)(10)Cl](+) films, where bpy is 2,2'-dipyridyl and PVP is poly(4-vinylpyridine). The maximum dry state conductivity observed is 3.5 +/- 0.3 x 10(3) and 8.7 +/- 0.1 x 10(2) S m(-1) where the polymer matrix is PVP and the metallopolymer, respectively. The percolation threshold is significantly lower for the nanoparticle loaded metallopolymer, 0.07 +/- 0.01, compared with PVP, 0.31 +/- 0.04. This result suggests that the osmium centers provide an enhanced conductivity pathway in the dry state. The redox properties of thin films of the composites deposited on microdisk platinum electrodes in contact with aqueous electrolyte have been investigated. The charge transport diffusion coefficient, D-CT, is approximately an order of magnitude larger for the composite containing the highest nanoparticle loading, 5.7 +/- 0.4 x 10(-9) cm(2) s(-1), than that found for the pure metallopolymer, 5.7 +/- 0.2 x 10(-10) cm(2) s(-1). A nanoparticle loading above the percolation threshold also promotes faster heterogeneous electron transfer increasing from 8.2 +/- 1.7 x 10(-5) to 4.0 +/- 0.2 x 10(-3) cm s(-1). (C) 2003 Elsevier B.V. All rights reserved.