Stable dispersions of gold (Au-0) nanoparticles are produced in a few commercially important thermoplastics using a novel surface infusion technique. The thermoplastic article is immersed in a dilute solution of HAuCl4 in a ternary solvent mixture held well below the melt-processing temperature of the plastic. Rapid infusion of plasticizing solvents and HAuCl4 is achieved for several thermoplastic polyurethane elastomers and an acrylic-pyrrolidinone copolymer. A second infusion of triethylamine, a reducing agent, produces Au-0 nanoparticles in a surface layer of (10-30 mu m) depth. Precipitation of Au-0 nanoparticles is arrested by the high viscosity of the plasticized polymer matrix, resulting in a stable dispersion, but formation of aggregates is possible in some plastics. The Au-0 particle size distribution can be manipulated by changing processing conditions that affect the formation of aggregates, such as the concentrations of HAuCl4 and plasticizers. POLYM. ENG. SCI., 50:120-127, 2010. (C) 2009 Society of Plastics Engineers