Catalytic activity of gold-platinum, gold-palladium, and platinum-palladium dendrimer nanocomposites for scavenging 1,1-diphenyl-2picrylhydrazyl (DPPH) radicals was investigated. The gold-platinum and gold-palladium dendrimer nanocomposites were prepared via simultaneous reduction by sodium borohydride in the presence of poly(amidoamine) (PAMAM) dendrimers with amine or carboxyl terminal groups. The particles were not mixtures of monometallic particles but alloyed bimetallic particles. Bimetallic particles exhibited higher catalytic activity than monometallic ones. (c) 2006 Elsevier Inc. All rights reserved.