Gold-platinum-silver (Au-Pt-Ag) ion mixtures produced nanoparticle alloys with an average particle size of 5 nm after co-reduction of metal ions by femtosecond laser irradiation of aqueous solutions in the presence of ammonia and polyvinylpyrrolidone, which was used as a stabilizer. Alloy formation was confirmed by analyzing the interplanar spacings measured by diffraction techniques; the interplanar spacings obtained showed good agreement with those derived from Vegard's law. The nanoparticles had elemental composition ratios close to the molar ratios of ions in the mixed solutions, implying a high reduction yield. High-resolution transmission electron microscopy images of nanoparticles revealed that the particles were crystalline and were not phase segregated. Binary nanoparticles from Au-Pt and Ag-Pt immiscible systems were also synthesized to confirm the applicability of this method to ternary systems. The formation of nanoalloys by intense femtosecond laser irradiation was possible due to the fast reduction of the mixed ions by solvated electrons and hydrogen radicals generated in situ during irradiation. (C) 2012 Elsevier Inc. All rights reserved.