Using gamma-irradiation-induced reduction in the field of a Co-60 gamma-ray source, colloidal silver and gold nanoparticles were prepared from their corresponding metal salts in aqueous solution and compared with those by chemical reduction. The radiation-based method provided silver nanoparticles with higher concentration and narrower size distribution than those obtained by chemical reduction method while there was no significant difference between the two strategies for the preparation of gold nanoparticles. gamma-Irradiation of 1.0 x 10(-3) M AgNO3 solution resulted in nearly 100 times more highly concentrated silver colloids than those by citrate reduction. Furthermore, the radiation method could lead to more highly concentrated silver colloids by simply increasing the concentration of AgNO3 solution up to 2.0 x 10(-2) M. The two metal nanoparticles prepared by the two different methods were characterized by UV-vis spectrophotometry and transmission electron microscopy (TEM), and compared regarding to their respective attainable concentrations and size distribution. (c) 2007 Elsevier B.V. All rights reserved.